(CNN) Hurricane Maria whipped Puerto Rico with Irma-level winds, drenched the island with Harvey-level flooding, crippled communications, decimated buildings and damaged a dam that puts downstream residents at risk of catastrophe.

But help has been slow to come to communities where the devastation is described as "apocalyptic," officials and residents argue.

Gov. Ricardo Rosselló said the island faces a humanitarian crisis. He urged Congress to approve a commensurate aid package as the US commonwealth, already hammered by a prolonged economic crisis , tries to get back on its feet.

The governor joined others in emphasizing that Puerto Ricans are American citizens.

"We need something tangible, a bill that actually answers to our need right now," he said. "Otherwise, there will be ... a massive exodus to the (mainland) United States."

Leading Democrats called for swift action to help the island.

"The Trump Administration must act immediately to make available additional Department of Defense resources for search-and-rescue operations, law enforcement and transportation needs," Pelosi said in a statement. "Our fellow Americans in Puerto Rico and the Virgin Islands deserve to know that their government will be there for them, without question or hesitation."

White House: Response 'anything but slow'

President Donald Trump has pledged federal help for Puerto Rico and the US Virgin Islands. A White House official said Trump is planning to visit Puerto Rico , but a date has not been set because of infrastructure concerns on the island.

Homeland Security Adviser Tom Bossert and FEMA administrator Brock Long were traveling to Puerto Rico, according to White House press secretary Sarah Sanders.

"The federal response has been anything but slow," Sanders said. "There's been an unprecedented push through of billions of dollars in federal assistance."

Airplanes and ships loaded with meals, water and generators have been arriving or are headed to Puerto Rico and other affected Caribbean islands, the Federal Emergency Management Agency said in a statement. More than 10,000 federal employees are in Puerto Rico and the US Virgin islands helping with research and rescue efforts and moving goods, FEMA tweeted.

10K+ empleados federales están en Puerto Rico & USVI ayudando con los esfuerzos de búsqueda y rescate y mover bienes. #Maria [📷: @USArmy] pic.twitter.com/nKAolxOdkM — FEMA en español (@FEMAespanol) September 25, 2017

In a tweet Sunday, Clinton said, "President Trump, Sec. Mattis, and DOD should send the Navy, including the USNS Comfort, to Puerto Rico now. These are American citizens."

President Trump, Sec. Mattis, and DOD should send the Navy, including the USNS Comfort, to Puerto Rico now. These are American citizens. https://t.co/J2FVg4II0n — Hillary Clinton (@HillaryClinton) September 24, 2017

Puerto Rico faces a more immediate danger.

The Guajataca Dam in the island's northwest corner is releasing water after suffering a "critical infrastructure failure" following the Category 5 storm.

"Some of the dam has fallen apart," Rosselló said. "Now we are making sure that we can assess if the other part will fall down as well. It represents a great danger for about an estimated 70,000 people."

Residents below the dam were told to evacuate on Friday, according to the National Guard. With more than 95% of wireless cell sites out of service, authorities had to physically go to thousands of homes to warn people of the potential collapse .

Rosselló said that while most people in the vicinity had evacuated, efforts were still underway to get people out in peripheral areas.

The Guajataca Dam suffered "infrastructure" damage following Hurricane Maria.

Communications cut

Without power and communications in much of the island, millions of people have been cut off from the world since Maria hit Wednesday.

"It is as if Puerto Rico got hit with the strength of Irma's winds, leaving a trail of devastation worse than much of the destruction Irma left in Florida," said CNN meteorologist Judson Jones.

"The rainfall in some areas of Puerto Rico rival the amounts of rain left by Harvey in Houston. And now they are contending with a dam disaster that is reminiscent of California's Oroville Dam crisis earlier this year."

After flying over Puerto Rico on Sunday, CNN's Leyla Santiago said residents could be seen along the highways searching for a cellphone signal.

"The island from above is a completely different color" due to the lack of trees, Santiago said, while pools are filled with black water and debris. The storm ripped the roofs of houses, exposing their interiors to the sky, she said.

Authorities who flew over the island Saturday were also stunned by what they saw. Roads are completely washed away and others are blocked by debris, isolating residents.

"It was devastating to see all that kind of debris in all areas, in all towns of the island," Jenniffer González, the island's nonvoting representative in Congress, told CNN.

Hurricane Maria ripped roofs off many houses.

Hospitals crippled

At least 10 people have been confirmed killed by the hurricane.

A doctor at Canovanas Medical Center -- one of the few hospitals with a working generator -- said they were running out of fuel to keep it going. Dr. Norbert Seda told CNN that the center only had 2-3 days left of medical supplies and medicine.

Culminamos el vuelo sobre el sureste de Puerto Rico. Algunas imágenes del impacto de #Maria en la infraestructura. pic.twitter.com/fWuQtS2qeg — Ricardo Rossello (@ricardorossello) September 24, 2017

None of the three hospitals CNN visited had running water and all said they had just days of supplies left.

However, earlier, Rosselló guaranteed that the people of Puerto Rico would have access to enough food and water to survive.

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

"We have centers that will distribute water and food, we've already started getting shipments. Today, as a matter of fact, we had a million liters of water come in to Puerto Rico. We have half a million servings of food and other resources." Rosselló also said the island has enough fuel for the next 20 days.

Roselló met with more than 50 mayors and representatives from across Puerto Rico on Saturday. Some said there have been incidents of looting in both homes and stores.