Media playback is unsupported on your device Media caption Why Hurricane Maria hit Puerto Rico so hard

US President Donald Trump has lifted shipping restrictions to help fuel and supplies reach storm-ravaged Puerto Rico, the White House has said.

Mr Trump "has authorized the Jones Act be waived for Puerto Rico", a statement said on Twitter.

Puerto Rico had pressed the US to lift the act, which limits shipping between coasts to US-flagged vessels.

The US territory is struggling with fuel, water and medical shortages one week after Hurricane Maria struck.

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The most powerful hurricane to hit Puerto Rico in nearly 90 years, Maria swept across the island last Wednesday.

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How bad is the situation?

Many of Puerto Rico's 3.4 million residents have been without electricity and other basic necessities since the storm struck.

The death toll was not as bad as the scores killed by Hurricane Irma - Maria claimed more than 30 lives in the Caribbean, including at least 16 in Puerto Rico.

But category four Maria knocked out the US territory's entire power grid, crippling its water and sewage treatment system.

More than 90% of cellular communication sites remain out of service, US officials say

Some 44% of the island's population do not have clean drinking water, the Pentagon says

Twenty-five of the island's 69 hospitals are not operational, said Homeland Security adviser Tom Bossert

An estimated 90% of all homes on the island are damaged

Almost 10,000 shipping containers filled with supplies were reportedly sitting in Puerto Rico's main port of San Juan on Thursday morning because of a lack of truck drivers.

Puerto Rico gets most of its fuel by ship from the US, and it has been under petrol rationing since the hurricane struck.

One resident, Juan Cruz, told Reuters news agency: "We can use more help. We are US citizens. We are supposed to be treated equally."

Ricardo Rossello, the island's governor, has called its devastation an unprecedented natural disaster.

Media playback is unsupported on your device Media caption US Navy evacuates residents from storm-devastated Dominica

How is the US responding?

The Federal Emergency Management Authority said it had delivered more than 4.4m meals and 6.5m litres of water to Puerto Rico and the US Virgin Islands by Wednesday.

But the transport of relief supplies has been hampered by roads rendered impassable by fallen trees or flooding.

The 1,000-bed US Navy hospital ship Comfort will arrive next week, after sailing from its home port in Virginia on Friday.

Some 10,000 federal officers, including 7,200 troops, are involved in the aid effort.

What is the Jones Act?

By waiving the Jones Act, the US will allow for more rapid delivery of aid to Puerto Rico.

The legislation, known formally as the Merchant Marine Act of 1920, requires goods ferried to US ports to be sent on ships that are built, owned and operated by Americans.

The regulation was created to promote the American commercial shipping industry.

But it has made the price of goods in Puerto Rico more expensive than those on the US mainland or other Caribbean islands.

The cost of living in Puerto Rico is also higher as a result.

Foreign goods must first be sent to the US mainland and transferred to American ships before they can be sent to US territories such as Puerto Rico.

This means aid from countries such as the nearby Dominican Republic cannot directly be sent to the devastated island.

The US waived the Jones Act during the recent Hurricanes Harvey and Irma to help ships quickly reach Texas and Florida.