President Donald Trump on Thursday gave his administration ten-out-of-ten for its response a hurricane that hammered Puerto Rico exactly one month ago, as 80 percent of the US island remained without power.

Meeting Puerto Rico's governor Ricardo Rossello in the Oval Office, Trump acknowledged the massive scale of the rebuilding effort, but defended his administration's response.

We have provided so much, so fast, we were actually there before the storm hit," Trump said. "They got hit dead center."

As well as ravaging the electricity grid, the storm knocked out bridges, closed roads and made clean water for drinking, cooking and bathing scarce.

Asked how he would rank the administration's response out of ten, Trump responded "I give ourselves a ten."

"We have done a really great job."

When Trump asked Rosello "did we do a great job?" the governor said that Trump had met all of his requests.

But he added that much more needed to be done to avoid a humanitarian disaster.

He said the authorities aim to have about 30% of the island back with power by the end of the month, and 50% by the middle of next month.

But he warned that without hope, Puerto Ricans -- who have the right to live in the continental United States -- would flee the island in large numbers, feeding an economic crisis.

"What's going to keep the people there and keep this going is knowing that we have the backing of the White House and knowing that we're going to have the backing of Congress," he said.

They need to know, he said, "that we can have the resources appropriate" to deal with the storm. "US citizens of Puerto Rico can come out of this catastrophe stronger than ever before."

- 'Not their fault' -

Trump had previously raised concerns on the island by warning that federal aid for Puerto Rico will not be open-ended.

But he indicated Thursday that a mixture of grants and loans could be found to rebuild, in particular, the electricity grid, which was in poor shape before the storm.

The federal government would have to be paid back before private bondholders, he added.

"We're helping a lot," Trump said. "We're doing that because we have an obligation to Puerto Rico, to humanity, to ourselves."

Trump also rowed back on some comments that appeared to blame Puerto Ricans for their plight.

"It's not the people's fault, they lost their house, they were devastated," he said.

"A person loses his or her house and then they can't go to work. If you lose your house, you know, it's hard to go and be a policeman, you are trying to have your family live."