Donald Trump gave Puerto Rico a sharp reminder of the billions of dollars of debt that it owes to Wall Street on Monday, saying it was in "deep trouble".

The island is battling a humanitarian crisis after being battered by Hurricane Maria last week.

Five days after the Category 4 storm slammed into Puerto Rico, many of the more than 3.4 million U.S. citizens 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.

The full extent of its plight was highlighted by a satellite image, released by the National Oceanic and Atmospheric Administration (NOAA), which showed a blackout affecting most of the island.

The Trump administration has tried to blunt criticism that its response to Hurricane Maria has fallen short of its efforts in Texas and Florida after the recent hurricanes there.

Mr Trump himself pointed out some differences between the two states and the island in a series of tweets Monday night.

"Texas & Florida are doing great but Puerto Rico, which was already suffering from broken infrastructure & massive debt, is in deep trouble."