The US government has declared that its relief efforts in Puerto Rico were succeeding, but people on the hurricane-devastated island said help was scarce and many residents were desperate for fresh water, food and electricity.

The complaints came eight days after Hurricane Maria slammed into the US territory of 3.4 million people, destroying much of the island's infrastructure.

"The federal response has been a disaster," said legislator Jose Enrique Melendez, a member of Governor Ricardo Rossello's New Progressive Party. "It's been really slow."

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He said US officials had focused more on making a good impression on members of the media gathered in the capital San Juan's convention centre than bringing aid to rural Puerto Rico.

"There are people literally just modelling their uniforms," Melendez said. "People are suffering outside."

President Donald Trump cleared the way for more supplies to reach Puerto Rico by issuing a 10-day waiver of federal restrictions on foreign ships delivering cargo to the island.

House Speaker Paul Ryan said the Federal Emergency Management Agency's disaster relief account would get a $6.7bn boost by the end of the week.

Presidential spokeswoman Sarah Huckabee Sanders said 10,000 government workers, including more than 7,000 soldiers, were helping Puerto Rico recover.

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Acting Homeland Security Secretary Elaine Duke declared "the relief effort is under control".

"It is really a good news story in terms of our ability to reach people," she told reporters in the White House driveway on Thursday.

However, outside San Juan, people said the comments from US officialdom were far from the truth.

"I have not seen any federal help around here," said Javier San Miguel, a 51-year-old accountant.

In the town of San Lorenzo, residents are collecting spring water to drink and taking turns cooking food for each other because they are running low on basic supplies.

In the nearby fishing town of Catano, authorities said they would open a distribution point over the weekend to hand out food and water.

"We need food," said Maritza Gonzalez, a 49-year-old government worker.