U.S. President Donald Trump says Puerto Rico is in "deep trouble" after being hit by Hurricane Maria and that its billions of dollars of debt to Wall Street and banks "must be dealt with." 

"Puerto Rico, which was already suffering from broken infrastructure & massive debt, is in deep trouble," Trump wrote in a series of posts on Twitter Monday night. 

Trump did not offer a pathway for dealing with Puerto Rico's debt of $72 billion US.

The U.S. territory filed the biggest government bankruptcy in U.S. history earlier this year.

Maria, the most powerful hurricane to hit Puerto Rico in nearly a century, devastated the Caribbean island when it struck with ferocious winds and torrential rains last week. 

Puerto Rico Gov. Ricardo Rossello on Monday asked for more government aid to avert a humanitarian crisis in the island, which is home to 3.4 million people.

The U.S. heightened its response to the crisis Monday, while the Trump administration sought to blunt criticism that its response has fallen short of it efforts in Texas and Florida after the recent hurricanes there.

Five days after the Category 4 storm slammed into Puerto Rico, many in the territory were still without adequate food, water and fuel. Flights off the island were infrequent, communications were spotty and roads were clogged with debris. Officials said electrical power may not be fully restored for more than a month. 

In Washington, officials said no armada of U.S. navy ships was headed to the island because supplies could be carried in more efficiently by plane. The Trump administration ruled out temporarily setting aside federal restrictions on foreign ships' transportation of cargo, saying it wasn't needed. The government had waived those rules in Florida and Texas until last week.

Democratic lawmakers with large Puerto Rican constituencies on the mainland characterized the response so far as too little and too slow. 

"Puerto Ricans are Americans," said Rep. Nydia Velazquez, of New York, who travelled to the island over the weekend to assess the damage. "We cannot and will not turn our backs on them." 

70,000 evacuate river valley

Trump said during an appearance in New York last week that Puerto Rico was "absolutely obliterated" and in "very tough shape." But over the weekend he made no mention of the humanitarian difficulties as he tweeted criticisms of NFL football players for their protests during the national anthem.

Rossello expressed his gratitude for the help so far, but also urged the U.S. Congress to fund an aid package to avert a humanitarian crisis. 

At a news briefing, Rossello also said that most of the people living near a crumbling dam on the island had been moved to safety. 

STORM-MARIA/PUERTORICO

An aerial view shows the damage to the Guajataca dam in Quebradillas, Puerto Rico, in the aftermath of Hurricane Maria. (Alvin Baez/Reuters)

There were growing concerns for some 70,000 people who live in the river valley below the Guajataca Dam in the island's northwest, where cracks were seen on Friday in the 88-year-old earthen structure. 

Rossello said he was working on the assumption that the 35-metre dam would collapse.

"I'd rather be wrong on that front than doing nothing and having that fail and costing people lives," he said in an interview with CNN. "Some of the dam has fallen apart, and now we're making sure that we can assess if the other part is going to fall down as well.... Most of the people in the near vicinity have evacuated." 

The fear of a potentially catastrophic dam break added to the immense task facing disaster relief authorities after Maria,
which was the second major hurricane to strike the Caribbean this month. The confirmed toll from Maria jumped to at least 49 on Monday, including 16 dead in Puerto Rico, several of whom drowned or were hit by flying debris.

Economic crisis worsens 

Many structures on the island, including hospitals, remained badly damaged and flooded. 

Rossello said on Monday that before the storms struck, he had been embarking on an aggressive fiscal agenda that included more than $1.5 billion in cuts. 

"This is a game changer," he told CNN. "This is a completely different set of circumstances. This needs to be taken into
consideration — otherwise there will be a humanitarian crisis." 

In a statement appealing for support from the U.S. government, Rossello said, "We ask the Trump administration and U.S. Congress to take swift action to help Puerto Rico rebuild." 

Helping Puerto Rico

Residents line up gas cans as they wait for a gas truck to service an empty gas station, in the aftermath of Hurricane Maria in Loiza, Puerto Rico. (Gerald Herbert/Associated Press)

In Washington, U.S. House of Representatives Speaker Paul Ryan said Congress was working with Trump's administration to ensure Puerto Rico was given necessary assistance. 

"Our fellow citizens in Puerto Rico remain in our prayers as we make sure they have what they need," he said in a statement. 

Relief package?

House Democratic leader Nancy Pelosi urged the Trump administration to deploy Defence Department resources for rescue operations, law enforcement and transportation in Puerto Rico and the U.S. Virgin Islands. 

Congress must also "swiftly" pass a relief package, she said in a statement. Republicans control the White House and both chambers of Congress. 

Singer Jennifer Lopez, whose parents are Puerto Rican, has pledged $1 million toward relief efforts, announcing Sunday that she would give money from her ongoing Las Vegas residency to various charities in the aftermath of Hurricane Maria. The 48-year-old Lopez says she still has family on the island that she has yet to hear from.

Fellow singer Ricky Martin has donated $100,000 to the relief effort and launched an online fundraiser. 

There are more than 10,000 federal staff, including more than 700 people from the Federal Emergency Management Agency (FEMA), doing recovery work in Puerto Rico and the U.S. Virgin Islands, according to FEMA. 

The National Hurricane Centre said Monday night that Maria was about 400 kilometres southeast of Cape Hatteras, N.C., with maximum sustained winds of 128 km/h, and was expected to pass east of the state's coast over the next couple of days.  

With files from The Associated Press