Hurricane Maria is currently pummelling Puerto Rico with 155mph winds after already leaving at least nine people dead in the Caribbean.

The Category 4 hurricane made landfall on the US territory early on Wednesday and is expected to last the island with life-threatening winds for up to 24 hours, forecasters said.

People calling local radio stations reported that doors were flying off hinges and a water tank flew away in the island's southern region.

Meanwhile, widespread flooding was reported in the capital of San Juan, with water running down one apartment's interior staircase.

"This is going to be an extremely violent phenomenon," Governor Ricardo Rossello said.

"We have not experienced an event of this magnitude in our modern history."

Puerto Rico had long been spared from a direct hit by hurricanes that tend to veer north or south of the island.

The last Category 4 hurricane landfall in Puerto Rico occurred in 1932, and the strongest storm to ever hit the island was San Felipe in 1928 with winds of 160mph.

More than 4,400 people were placed in shelters by late Tuesday, along with 105 pets, Governor Rossello said.

Troops and residents in the British Virgin Islands are also bracing themselves for Maria's wraith, having been battered by Hurricane Irma earlier this month.

Emergency steps are being undertaken on the BVI to prepare for the onslaught.

Relief workers are racing to secure debris left strewn across the islands after Irma, as loose items have the potential to make the coming hurricane "more hazardous" if it is picked up by high winds.

Maria has killed two people in the French Caribbean island of Guadeloupe and two people aboard a boat were reported missing off La Desirade island, just east of Guadeloupe, officials said.

The storm also blew over the tiny eastern Caribbean island of Dominica late Monday, where Prime Minister Roosevelt Skerrit sent out a series of dramatic posts on his Facebook page, including that his own roof had blown away.

"The winds are merciless! We shall survive by the grace of God," Mr Skerrit wrote before communications went down.