San Juan, Puerto Rico (CNN) A mountain of food, water and other vital supplies has arrived in Puerto Rico's main Port of San Juan.

But a shortage of truckers and the island's devastated infrastructure are making it tough to move aid to where it's needed most, officials say.

At least 10,000 containers of supplies -- including food, water and medicine -- were sitting Thursday at the San Juan port, said Jose Ayala, the Crowley shipping company's vice president in Puerto Rico.

Part of the reason for the distribution backlog is that only 20% of truck drivers have reported back to work since Hurricane Maria swept through, according to a representative for Puerto Rican Gov. Ricardo Rosselló.

On top of that, a diesel fuel shortage and a tangle of blocked roads mean the distribution of supplies is extremely challenging. Even contacting drivers is a problem because cell towers are still down.

"When we say we that we don't have truck drivers, we mean that we have not been able to contact them," Rosselló said.

On Thursday the White House authorized a 10-day waiver of the Jones Act , a federal law that limits shipping to US ports by foreign vessels. Puerto Rico's governor and other US officials had argued that a waiver would expedite supplies to the island.

But as Ayala has indicated, shipping companies already have aid and supplies either waiting at the port to be delivered -- or held up at ports on the US mainland.

Of the 3,000 containers that Crowley alone had sent to San Juan's port as of Wednesday, only 4% had been dispatched from there, Ayala said.

'This hurricane was catastrophic'

Ayala said the company can't get enough truck drivers or trucks filled up with diesel to pick up supplies for distribution across the island.

Photos: Hurricane Maria slams the Caribbean Photos: Hurricane Maria slams the Caribbean An apartment building is missing a wall in San Juan, Puerto Rico, on Monday, September 25, nearly a week after Hurricane Maria devastated the US commonwealth. Power is still out in most places, and communications remain almost nonexistent on the island of 3.4 million people. Hide Caption 1 of 36 Photos: Hurricane Maria slams the Caribbean Yancy Leon rests at the Luis Muñoz Marin International Airport near San Juan on September 25. She's been waiting in line for two days to get a flight out. Hide Caption 2 of 36 Photos: Hurricane Maria slams the Caribbean An aerial view shows the flooding in San Juan on September 25. Hide Caption 3 of 36 Photos: Hurricane Maria slams the Caribbean People collect water from a natural spring created by landslides in Corozal, Puerto Rico, on Sunday, September 24. Puerto Rican Gov. Ricardo Rosselló said the island faces a humanitarian crisis. Hide Caption 4 of 36 Photos: Hurricane Maria slams the Caribbean An aerial view shows a flooded neighborhood in Catano, Puerto Rico, on Friday, September 22. Hide Caption 5 of 36 Photos: Hurricane Maria slams the Caribbean A man cleans a muddy street in Toa Baja, Puerto Rico, on September 22. Hide Caption 6 of 36 Photos: Hurricane Maria slams the Caribbean A man walks on a highway divider while carrying his bicycle through San Juan, Puerto Rico, on Thursday, September 21. Hide Caption 7 of 36 Photos: Hurricane Maria slams the Caribbean A shack is destroyed in San Juan on September 21. Hide Caption 8 of 36 Photos: Hurricane Maria slams the Caribbean A gas station's sign is damaged in Punta Cana, Dominican Republic, as the hurricane passed just north of the country on September 21. Hide Caption 9 of 36 Photos: Hurricane Maria slams the Caribbean Rescue workers drive through a flooded road in Humacao, Puerto Rico, on Wednesday, September 20. Hide Caption 10 of 36 Photos: Hurricane Maria slams the Caribbean A mattress that fell from the third floor is surrounded by debris outside a San Juan apartment complex on September 20. Hide Caption 11 of 36 Photos: Hurricane Maria slams the Caribbean Damage is seen in Roseau, Dominica, on September 20. Hide Caption 12 of 36 Photos: Hurricane Maria slams the Caribbean People walk through the destruction in Roseau on September 20. Hide Caption 13 of 36 Photos: Hurricane Maria slams the Caribbean San Juan is shrouded in darkness after the hurricane knocked out power to the entire island of Puerto Rico. Hide Caption 14 of 36 Photos: Hurricane Maria slams the Caribbean Power lines are scattered across a road in Humacao, Puerto Rico, on September 20. Hide Caption 15 of 36 Photos: Hurricane Maria slams the Caribbean Residents move aluminum panels from an intersection in Humacao on September 20. Hide Caption 16 of 36 Photos: Hurricane Maria slams the Caribbean Rescue vehicles are trapped under an awning in Humacao on September 20. Hide Caption 17 of 36 Photos: Hurricane Maria slams the Caribbean Trees are toppled outside the Roberto Clemente Coliseum in San Juan on September 20. Hide Caption 18 of 36 Photos: Hurricane Maria slams the Caribbean Members of a rescue team embrace as they wait to help in Humacao on September 20. Hide Caption 19 of 36 Photos: Hurricane Maria slams the Caribbean A tree is damaged in Fajardo, Puerto Rico, on September 20. Hide Caption 20 of 36 Photos: Hurricane Maria slams the Caribbean Debris is strewn across a Fajardo street on September 20. Hide Caption 21 of 36 Photos: Hurricane Maria slams the Caribbean A woman closes her property in Naguabo, Puerto Rico, hours before Maria's arrival. Hide Caption 22 of 36 Photos: Hurricane Maria slams the Caribbean People take shelter at Puerto Rico's Humacao Arena on Tuesday, September 19. Hide Caption 23 of 36 Photos: Hurricane Maria slams the Caribbean Two girls play on cots at the Humacao Arena. Hide Caption 24 of 36 Photos: Hurricane Maria slams the Caribbean Waves crash in San Juan as the hurricane neared Puerto Rico on September 19. Hide Caption 25 of 36 Photos: Hurricane Maria slams the Caribbean People pray in Humacao on September 19. Hide Caption 26 of 36 Photos: Hurricane Maria slams the Caribbean A street is flooded in Pointe-a-Pitre, on the French Caribbean island of Guadeloupe, on September 19. Hide Caption 27 of 36 Photos: Hurricane Maria slams the Caribbean People stand near debris at a restaurant in Le Carbet, Martinique, on September 19. Hide Caption 28 of 36 Photos: Hurricane Maria slams the Caribbean People in Luquillo, Puerto Rico, board up windows of a business on September 19. Hide Caption 29 of 36 Photos: Hurricane Maria slams the Caribbean A boat is overturned off the shore of Sainte-Anne, Guadeloupe, on September 19. Hide Caption 30 of 36 Photos: Hurricane Maria slams the Caribbean Cars line up at a gas station in San Juan on September 19. Hide Caption 31 of 36 Photos: Hurricane Maria slams the Caribbean A motorist drives on the flooded waterfront in Fort-de-France, Martinique, on September 19. Hide Caption 32 of 36 Photos: Hurricane Maria slams the Caribbean Floodwaters surround cars in Pointe-a-Pitre on September 19. Hide Caption 33 of 36 Photos: Hurricane Maria slams the Caribbean Soldiers patrol a street in Marigot, St. Martin, as preparations were made for Maria on September 19. Hide Caption 34 of 36 Photos: Hurricane Maria slams the Caribbean People buy provisions in Petit-Bourg, Guadeloupe, as the hurricane approached on Monday, September 18. Hide Caption 35 of 36 Photos: Hurricane Maria slams the Caribbean Customers wait in line for power generators at a store in San Juan on September 18. Hide Caption 36 of 36

"The problem has been with the logistics, the parts of the supply chain that move the cargo from our terminal to the shelves or to the tables of the people in Puerto Rico," Ayala said Wednesday. "This hurricane was catastrophic."

Meanwhile, Puerto Ricans are waiting hours in line to get gas, food and cash. Gas stations and supermarkets are rationing supplies, while banks are running low on cash.

Natalia Manteiga waited outside a supermarket Wednesday in Old San Juan that was letting in a few people at a time. She wanted to get water, tuna, and Chef Boyardee for her two children and her husband -- who had waited for hours Tuesday to get $20 worth of gas.

With stifling humidity and temperatures in the high 90s, it started to rain on Mantiega and dozens of other hopeful shoppers trying to get food.

Manteiga, who works for a tourism firm, said she's running low on cash, too.

"It's difficult when you have kids. You want to make sure they have enough food," said Manteiga. "They told me the banks are refilling, but we don't know and the lines are very long."