By Nicole Chavez and Susannah Cullinane, CNN

(CNN) -- The devastation wrought by Hurricane Maria continues to cripple Puerto Rico, with fears a damaged dam in the island's northwest may break.

The Guajataca Dam is "releasing water" after suffering "infrastructure damage" following the Category 5 storm, Puerto Rico Gov. Ricardo Rosselló told CNN late Sunday.

"Right now, as it stands, a couple of hours after I went through Isabela, part of the dam did break it is releasing water," Rosselló said. "And that dam is partly concrete, partly soil. So as water runs through, erosion starts having its toll on the dam and my concern is at some point it'll break."

An engineer was assessing the site and seeing what steps could be taken to mitigate the risk, Rosselló said.

A flood warning for western Puerto Rico has been extended until 8.15 a.m. ET Monday, according to a tweet late Sunday by the National Weather Service of San Juan.

About 70,000 people in the area of the Guajataca 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 residents to warn them of the potential collapse.

Communications cut

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

Flying over Puerto Rico 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 had ripped the roofs of houses, exposing their interiors to the sky, she said.

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.

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

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

"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.

He issued a plea to US Congress for a suitable aid package as the US territory recovers from the damage caused by Hurricane Maria. "Congress can act. If they don't act, my fear is that we will see massive migration, it will be depleting the human resource here in Puerto Rico and it will be effecting demographic change in the United States as well."

Authorities flew over the island Saturday, and were 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 non-voting representative in Congress told CNN.

"We never expected to have a lot of debris in so many areas. A lot of roads are closed, older ones are just gone," she added.

Roselló met with more than 50 mayors and representatives from across Puerto Rico on Saturday. Some described the conditions in their communities as "apocalyptic" and said there have been incidents of looting in both homes and stores.

Army, more federal aid coming

US President Donald Trump has pledged federal help for Puerto Rico and the US Virgin Islands.

The Puerto Rico Federal Affairs Administration said 4,000 members of the US Army Reserves have been deployed to the island to help with Hurricane Maria recovery.

"Federal partners are aggressively working to meet and overcome challenges to opening ports and restoring power to bring additional life-saving commodities and personnel into disaster-affected areas," the Federal Emergency Management Agency said in a statement.

Several flights and sea vessels with meals, water and generators have been arriving or are headed to Puerto Rico and other Caribbean islands affected, the agency said.

Brock Long, the FEMA director, said on Twitter Sunday he would visit Puerto Rico and the US Virgin Islands on Monday.

Maria marching north

Meantime, the US East Coast bracing for high winds and treacherous surf from Hurricane Maria, days after the storm caused widespread devastation in the Caribbean.

Early Monday the National Hurricane Center said Maria was expected to pass "well east" of the southeast coast during the next day or so.

A Tropical Storm Watch is in effect for north of Surf City, North Carolina, to the Virginia border, as well as North Carolina's Albemarle and Pamlico Sounds. A Storm Surge Watch is in effect for Cape Lookout to Duck.

"The combination of a dangerous storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters moving inland from the shoreline," the center warned, while dangerous swells were expected to increase along the Mid-Atlantic coast.

The storm hit Dominica, Puerto Rico, the Dominican Republic, the US Virgin Islands and the Turks and Caicos, a British overseas territory.