The White House's homeland security adviser defended the Trump administration's relief efforts in Puerto Rico in the wake of Hurricane Maria, which destroyed much of the island's infrastructure and left many residents desperate for fresh water, power, food and other supplies.

Tom Bossert, answering reporter questions at a briefing, said that the decision Thursday to waive federal restrictions on foreign ships' transportation of cargo to the hurricane-ravaged American territory was made at the right time. 

"In this particular case, we had enough capacity of U.S.-flagged vessels to take more than or to exceed the requirement in need," in Puerto Rico, Bossert told reporters.

The Jones Act is a little-known federal law that prohibits foreign-flagged ships from shuttling goods between U.S. ports. 

Republicans and Democrats had for days pushed President Donald Trump to waive the Jones Act, saying it could help get desperately needed supplies delivered to the island more quickly and at less cost. 

White House press secretary Sarah Sanders said in a Twitter post Thursday that Trump, at the request of Puerto Rica Gov. Ricardo Rossello, "authorized the Jones Act be waived for Puerto Rico. It will go into effect immediately."

Puerto Rico's government had sought a waiver of the law to ensure as many supplies as possible, including badly needed fuel, quickly reach the island of 3.4 million people.

Rossello retweeted Sanders's announcement with a "Thank you @POTUS" — referring to Trump's official Twitter handle.

The shipping restrictions will be lifted for 10 days, the Department of Homeland Security said. 

"This waiver will ensure that over the next 10 days, all options are available to move and distribute goods to the people 
of Puerto Rico. It is intended to ensure we have enough fuel and commodities to support lifesaving efforts, respond to the storm, and restore critical services and critical infrastructure operations in the wake of these devastating storms," Elaine Duke, acting homeland security secretary, said in a statement. 

Brock Long, the administrator of the Federal Emergency Management Agency (FEMA), said he was dissatisfied with the 
federal response, but that relief operations had been hampered by damage to the air traffic control system, airports and ports.

Maria struck Puerto Rico on Sept. 20, knocking out power to the entire island, causing widespread flooding and major damage to homes and infrastructure.

The U.S. government has periodically lifted the Jones Act for a temporary period following violent storms, including after hurricanes Harvey and Irma, which hit Texas and Florida in late August and earlier this month.

STORM-MARIA/PUERTORICO-WATER

People fill containers with water at an area hit by Hurricane Maria in Canovanas, Puerto Rico. On Thursday, the U.S. government agreed to waive shipping restrictions to increase the flow of aid to the island. (Carlos Garcia Rawlins/Reuters)

Even as federal emergency management authorities and the U.S. military have stepped up relief efforts, many residents have voiced exasperation at the prolonged lack of electricity, reliable supplies of drinking water and other essentials.

"The situation is not allowing things to move as quickly as we would all like," Long said.

"We will not be satisfied until we stabilize the situation, which is why we work day in and day out, hour after hour, to try to alleviate the situation."

Praise for Trump

Rossello has strongly praised Trump's response, defending the Republican administration against complaints of being slow to act and showing too little concern.

"The president has been very diligent; he has been essentially talking to us every day," the governor said in an interview with MSNBC on Thursday.

A member of Rossello's New Progressive Party disagreed.

STORM-MARIA/PUERTORICO-WATER

People queue to fill containers with water from a tank truck in Canovanas, Puerto Rico. (Carlos Garcia Rawlins/Reuters)

"The federal response has been a disaster," said lawmaker Jose Enrique Melendez. "It's been really slow." He said the Trump administration had focused more on making a good impression on members of the media gathered at San Juan's convention centre than bringing aid to rural Puerto Rico.

Critics have said Puerto Rico is not getting the same response as it would if it were a U.S. state, even though its residents are U.S. citizens.

Financial assistance needed

The U.S. military said it was sending a three-star general to Puerto Rico to help direct the hurricane response. Lt.-Gen. Jeff Buchanan was to arrive later Thursday.

Military assistance includes assessing the needs of the island's hospitals, trying to set up communications with each of the 78 municipalities and establishing a plan for distributing food and water, the Pentagon said Wednesday.

The military had delivered fuel to nine hospitals and helped establish more than 100 distribution centres for food and water on the island, the Pentagon said on Thursday.

It also was shipping a large generator to power a radar centre to help air traffic control in San Juan and other airports. Five of six priority sea ports were open, although some had restrictions on the size of the vessel or were for daylight use only, the Pentagon said.

A barge with 100 defence trucks carrying diesel and gasoline was expected to arrive in San Juan by Monday.