Hurricane Earl was upgraded to a Category 4 storm Monday as it lashed the northeastern Caribbean and set a course for eastern United States and Canada later this week.

The still-growing storm, with winds of 215 km/h, was upgraded by the U.S. National Hurricane Center at 5 p.m. ET. The centre said some fluctuations in strength are likely over the next 24 to 48 hours.

"A turn to the north is still expected, but is being forecast to happen later and later. This means that more of the U.S. east coast could potentially be affected by Earl, from South Carolina to Maine," said CBC meteorologist Natasha Ramsahai.

"After that, most forecast models are still bringing Earl as a potential Category 1 storm to the Canadian Maritimes for the Labour Day long weekend. There is still a chance that Earl could be kicked out to the east of Atlantic Canada, so we will have to wait another couple of days to better forecast this long-term track."

Meanwhile, tropical storm Fiona has formed hot on Earl's heels and will likely take the same path. The forecast is for Fiona to stay at tropical-storm strength, however, and not become a hurricane, Ramsahai said.

At 11 p.m. ET, Earl was centred 170 kilometres north of Puerto Rico and was moving west-northwest at 22 kilometres an hour. Its forecast path would take it east of the Turks and Caicos Islands on Tuesday night.

In Antigua, wind and rain destroyed at least one home, though there were no reports of critical injuries. Emergency response officials said about 350 people were in shelters. Local weather authorities reported at least 13 centimetres of rain and three-metre waves.

In St. Maarten, the storm toppled trees, damaged roofs and knocked out electricity to much of the island. Heavy gusts of wind swirled debris across streets that were empty due to a government-imposed curfew.

Cruise lines diverted ships to other ports, and flights were cancelled across Puerto Rico and the eastern Caribbean.

The U.S. Virgin Islands imposed a curfew from 6 p.m. Monday to 5:30 a.m. Tuesday for the islands of St. Thomas and St. John. Police Commissioner Novelle Francis said anyone found on the street during those hours without a pass will be taken into custody.

A tropical storm warning was in effect for Puerto Rico, the U.S. Virgin Islands, the British Virgin Islands and the Turks and Caicos Islands.

Earl has grown rapidly in strength, fuelled by warm ocean temperatures of 30 C.

Earl could bring battering waves and storm surges of up to 1.2 metres above normal on some islands, as well as downpours that threaten to unleash flash floods and mudslides.

Forecasters said there is a chance the hurricane could brush the U.S. Mid-Atlantic region toward the end of the week, with its closest approach to North Carolina on Thursday or Friday.

Meanwhile, Hurricane Danielle weakened to a tropical storm, with winds of 110 km/h, and is forecast to continue losing strength as it moves over the North Atlantic.

A satellite image taken Sunday afternoon shows Hurricane Danielle, located northeast of Bermuda. To the south, Hurricane Earl is shown east of Antigua. Earl is forecast to strengthen over the next couple of days. (Weather Underground/Associated Press) With files from The Associated Press