(CNN) Haiti had only just begun rebuilding from a devastating earthquake six years ago when Hurricane Matthew tore through the small Caribbean nation on Tuesday, killing hundreds in its path and inundating entire villages.

Once again much of the country is a disaster zone, with powerful Matthew shredding homes and engulfing communities in knee-deep water that is taking time to recede.

At least 300 people have died since Matthew made landfall in Haiti on Tuesday as a Category 4 hurricane, according to Paul Altidor, Haitian ambassador to the United States.

"We expect unfortunately that number to rise a little bit as we begin to access communities, regions that were inaccessible because of the roads, because of the bridges that fell due to the hurricane," Altidor told CNN's Wolf Blitzer.

Communication is still an issue in Southern Haiti, where winds of 125 mph (200 kph) destroyed homes, flooded villages and cut off the island from the rest of the country.

"The southern peninsula has been devastated," said US Navy Rear Adm. Cedric Pringle, commander of the Joint Task Force Matthew, after conducting an aerial tour of the destruction.

About 350 military personnel will be on the ground in Haiti by Saturday, Pringle said Friday in a briefing from Port-au-Prince. He's in the Haitian capital to kick start humanitarian and disaster relief assistance to the country.

Ships from the Netherlands, France and possibly from the United Kingdom will also help, he said.

As the hurricane brushed the Florida coast Friday, US President Barack Obama urged Americans to donate to the American Red Cross and other philanthropic organizations to help Haiti and other affected countries.

"We know that hundreds of people ... lost their lives and that they're going to need help rebuilding," he said at the White House.

Concern over food security

Photos: Hurricane Matthew pummels Haiti A man stands in the remnants of a house destroyed by Hurricane Matthew in the southern town of Les Cayes on Monday, October 10. Matthew wreaked havoc in Haiti, killing hundreds, destroying homes and knocking out electricity in the impoverished Caribbean nation. More than 1.4 million people are in need of urgent assistance, a UN official says. Hide Caption 1 of 37 Photos: Hurricane Matthew pummels Haiti Two young men who lost their homes awake from a tent in the courtyard of a school where they took shelter in Port Salut on October 10. Hide Caption 2 of 37 Photos: Hurricane Matthew pummels Haiti A woman sits in debris where her house once stood in Les Cayes on October 10. Hide Caption 3 of 37 Photos: Hurricane Matthew pummels Haiti A group works to clear debris from the streets in Les Anglais on October 10. Hide Caption 4 of 37 Photos: Hurricane Matthew pummels Haiti A man uses salvaged material to build a makeshift roof for his damaged house in Port-a-Piment on October 10. Hide Caption 5 of 37 Photos: Hurricane Matthew pummels Haiti People sick with cholera receive medical assistance at a hospital in Jeremie on October 10. The destruction from Matthew has accelerated the cholera epidemic in Haiti and undermined strides made in fighting the waterborne disease, the country's leader says. Hide Caption 6 of 37 Photos: Hurricane Matthew pummels Haiti People cross one of the many southern coastal rivers where bridges were knocked out or damaged near Port-a-Piment on October 10. Hide Caption 7 of 37 Photos: Hurricane Matthew pummels Haiti People pass damaged buildings in a seaside fishing neighborhood of Port Salut on Sunday, October 9. Hide Caption 8 of 37 Photos: Hurricane Matthew pummels Haiti People bathe and wash clothes in a river that runs through Roche-à-Bateaux on October 9. Concerns are rising in the storm's aftermath about cholera, caused by the ingestion of contaminated water or food. Hide Caption 9 of 37 Photos: Hurricane Matthew pummels Haiti US soldiers unload bags of food from a helicopter in the hard-hit coastal city of Jeremie on October 9. Hide Caption 10 of 37 Photos: Hurricane Matthew pummels Haiti Worshippers pray at a Jeremie church destroyed by Matthew on October 9. Hide Caption 11 of 37 Photos: Hurricane Matthew pummels Haiti A cholera patient receives treatment at a state hospital in Jeremie on October 9. Hide Caption 12 of 37 Photos: Hurricane Matthew pummels Haiti Family members react during the funeral of Roberto Laguerre, 32, on Saturday, October 8, in Jeremie. Laguerre was killed when the hurricane struck. Hide Caption 13 of 37 Photos: Hurricane Matthew pummels Haiti Andrenne Joseph dries her clothes near the remains of her house in Jeremie on October 8. Hide Caption 14 of 37 Photos: Hurricane Matthew pummels Haiti Residents of Jeremie wait on the shore October 8 as a boat with water and food from the "Mission of Hope" charity arrives. Jeremie appears to be the epicenter of Haiti's growing humanitarian crisis in the wake of the storm. Hide Caption 15 of 37 Photos: Hurricane Matthew pummels Haiti Corn salvaged from destroyed crops dries in the sun Saturday after Hurricane Matthew swept through Jeremie. Hide Caption 16 of 37 Photos: Hurricane Matthew pummels Haiti People unload food and water from a "Mission of Hope" charity boat Saturday after Hurricane Matthew swept through Jeremie. Hide Caption 17 of 37 Photos: Hurricane Matthew pummels Haiti An aerial view of damage to the small village of Casanette near Baumond, Haiti on Saturday. The full scale of the devastation in rural Haiti is becoming clear in the days after Hurricane Matthew leveled huge swaths of the country's south. Hide Caption 18 of 37 Photos: Hurricane Matthew pummels Haiti Haitians gather along a flooded street in Haiti on Friday, October 7. Hide Caption 19 of 37 Photos: Hurricane Matthew pummels Haiti Palm trees lie flattened on the ground after high winds knocked them over. Hide Caption 20 of 37 Photos: Hurricane Matthew pummels Haiti Rubble lies in the street in the aftermath of the storm. Hide Caption 21 of 37 Photos: Hurricane Matthew pummels Haiti Residents carry a coffin containing the remains of a pregnant woman, a victim of Hurricane Matthew, in Jeremie on Friday, October 7. People across southwest Haiti were digging through the wreckage of their homes Friday, salvaging what they could of their meager possessions. Hide Caption 22 of 37 Photos: Hurricane Matthew pummels Haiti An aerial view shows destruction caused by Hurricane Matthew in Jeremie, Haiti, on Friday, October 7. The damage from Hurricane Matthew was especially brutal in southern Haiti, where sustained winds of 130 mph punished the country. Hide Caption 23 of 37 Photos: Hurricane Matthew pummels Haiti Damaged homes are shown on Friday, October 7, in Haiti, where the death toll is in the hundreds. Hide Caption 24 of 37 Photos: Hurricane Matthew pummels Haiti A young man stands near the cathedral damaged by Hurricane Matthew, in Jeremie, Haiti, on October 7. Hide Caption 25 of 37 Photos: Hurricane Matthew pummels Haiti A man dries toys recovered from the debris left by Hurricane Matthew in Les Cayes, Haiti, on Thursday, October 6. Hide Caption 26 of 37 Photos: Hurricane Matthew pummels Haiti A girl washes mud from her feet after Hurricane Matthew passed through Les Cayes, Haiti, on October 6. Hide Caption 27 of 37 Photos: Hurricane Matthew pummels Haiti Fallen trees litter the ground outside a damaged church in Les Cayes on October 6. Hundreds of people have been killed in Haiti, the Dominican Republic and St. Vincent and the Grenadines, officials said, with the death toll expected to rise. Hide Caption 28 of 37 Photos: Hurricane Matthew pummels Haiti Girls wade through a flooded street in Les Cayes on October 6. Hide Caption 29 of 37 Photos: Hurricane Matthew pummels Haiti Two days after the storm, authorities and aid workers in Haiti still lack a clear picture of what they fear is the country's biggest disaster in years. Hide Caption 30 of 37 Photos: Hurricane Matthew pummels Haiti Saint Anne Church in Les Cayes is reduced to ruins. In the wake of the storm, the Electoral Commission postponed the country's presidential election, which had been scheduled for Sunday. Hide Caption 31 of 37 Photos: Hurricane Matthew pummels Haiti Residents repair their homes in Les Cayes. Hide Caption 32 of 37 Photos: Hurricane Matthew pummels Haiti Children sit inside a damaged church in Saint-Louis on Wednesday, October 5. Hide Caption 33 of 37 Photos: Hurricane Matthew pummels Haiti Men push a motorbike through a flooded street in Leogane on October 5. More than 300,000 people are in shelters across the country, the United Nations said.

Hide Caption 34 of 37 Photos: Hurricane Matthew pummels Haiti A man carries a woman across a river at Petit Goave on October 5. A bridge collapsed because of the storm. Hide Caption 35 of 37 Photos: Hurricane Matthew pummels Haiti A woman cleans her flooded home following the overflowing of La Rouyonne River on October 5 in Leogane. Residents could face risks from standing water. Haiti is still recovering from a cholera outbreak after the devastating 2010 earthquake. Hide Caption 36 of 37 Photos: Hurricane Matthew pummels Haiti Nice Simon, the mayor of Tabarre, holds a baby on October 3, as she helps evacuate the area along a river. Hide Caption 37 of 37

The bridge collapse in Petit Goave cut responders off from road access.

For now, the focus is just reaching victims, because the only bridge linking the capital Port-au-Prince to the worst-affected region in the southwest had completely collapsed, said Ariel Dominique, head of community affairs at the Haitian Embassy in Washington.

She said crews are working on that bridge that spans the Rivière la Digue in Petit-Goâve to make it passable for large-scale aid deliveries.

Conduit roads too are blocked by collapsed palm trees and debris, forcing agencies to consider air dropping of supplies as the skies clear and flying becomes a safer option.

Grand' Anse, and its capital Jeremie, is one of the worst affected areas, she said.

There was also extensive damage to crops along swaths of southern Haiti.

"We have nothing left to survive on, all the crops have gone, all fruit trees are down, I don't have a clue how this is going to be fixed," said Marc Soniel Noel, the deputy mayor of Chantal in the affected region.

"We're really concerned about food security," said John Hasse, National Director for World Vision, a US based humanitarian organization. He is currently in Haiti.

"A large portion of Haiti's food is produced in the south where the damage is most severe. It is a large breadbasket for the country. We expect to see food shortages and/or price spikes throughout the country in the coming weeks and months. This has the potential for creating not only great need but also increased violence and instability."

Residents take a mattress to a shelter after homes were destroyed in Les Cayes, Haiti.

Shelters crammed

Hurricane Matthew's ferocious impact left 350,000 people in need of assistance. The country's civil protection authority said that 186 people were injured and more than 61,000 people were now in 192 temporary shelters.

There was a "massive influx" of people to the shelters, which are struggling to find space for people cramming together to sleep on the floor, said CARE USA emergency communications manager Holly Frew.

"The priority is to get food and water to these people. Of course aid agencies like us had supplies pre-positioned before the storm, but there's only so much you can do in a storm this size, and as the the number of centers has more than doubled, the need has risen," Frew said.

She explained that the people in the affected region had already been suffering from drought before the hurricane hit.

"People have lost a lot. Some of those who bore the brunt of the storm are still in a state of shock. But some caught in the eye of the storm are feeling lucky to be alive."

A woman stands in a field of destroyed trees on Thursday.

Haitians wait to cross the river in Petit Goave where a bridge collapsed cutting off a main route to the devastated south of the country

The devastated town of Jeremie, west Haiti, in the aftermath of the hurricane.

Cholera epidemic could worsen

Images showed residents wading through muddy waters and farm fields choked with flood waters as crops floated lifelessly.

The impact of the hurricane immediately raised public health concerns, especially about the availability of clean water, food and shelter.

Aid agencies say 80% of people in the worst affecetd areas have lost their homes.

Partners in Health warned that the hurricane would likely worsen the country's cholera epidemic.

"Though the storm has passed, experience tells us that the worst is yet to come." PIH's Dr. Charles-Patrick Almazor: https://t.co/dZRutnLhYT — Partners In Health (@PIH) October 6, 2016

Dave Brodsky, president of Chanje Movement, a California-based church partnership that has been working in Haiti since the 2010 earthquake, said it was the "poorest of the poor" that had been worst hit by the flooding.

The Pan American Health Organization sent epidemiologists with cholera experience this week to Haiti.

Largest humanitarian crisis since 2010 earthquake

UNICEF had warned on Wednesday that Haiti is facing the largest humanitarian crisis since the 2010 earthquake, which killed at least 220,000, injured 300,000 and displaced 1.5 million people.

Haiti was only just beginning the development phase to rebuild infrastructure following that earthquake, said Ines Brill, the International Federation of Red Cross and Red Crescent Societies representative for Haiti.

"This is an emergency after an emergency, which makes things more complex than a typical disaster," she told CNN.

Haitian officials postponed the presidential elections, which had been scheduled for Sunday, due to the hurricane.