The US National Hurricane Centre said the centre of the storm, now called Post-Tropical Cyclone Fiona, was crossing eastern Nova Scotia, bringing high winds and heavy rains.

The storm had weakened somewhat as it travelled north. As at 7 pm AEST the storm was about 255 km northeast of Halifax, carrying maximum winds of 150 kph and barrelling north at around 43 kph, the Centre said.

Experts predicted high winds, storm surges and heavy rainfall from Fiona. Although a gradual weakening was forecast during the next couple of days, Fiona was expected to maintain hurricane-force winds until Saturday afternoon.

Formerly designated a hurricane, the storm battered Caribbean islands earlier in the week, killing at least eight people and knocking out power for virtually all of Puerto Rico's 3.3 million people during a sweltering heat wave. Nearly a million people remained without power five days later.

Canadian Prime Minister Justin Trudeau delayed his departure for Japan, where he was to attend the funeral of former Prime Minister Shinzo Abe, to receive briefings and support the government's emergency response.

A hurricane warning was in effect for much of central Nova Scotia and Prince Edward Island, home to more than 150,000 people, and parts of Newfoundland.

Canadian Hurricane Centre meteorologist Ian Hubbard said on Friday the effects of Fiona would be felt over a wide area.

"The weather that's associated with it in terms of the rain and where all the strong winds are, it's going to be over a much larger area," he said.

"Many, many places away from the centre of the storm are still going to be seriously impacted from this," Hubbard told Reuters.

Canadian authorities sent emergency alerts in Nova Scotia and Prince Edward Island, warning of severe flooding along shorelines and extremely dangerous waves. People in coastal areas were advised to evacuate.

The storm could prove more ferocious than the benchmarks of Hurricane Juan in 2003 and Hurricane Dorian in 2019, Canadian Hurricane Centre meteorologist Bob Robichaud told a briefing.

The country's two largest carriers, Air Canada and WestJet Airlines, suspended regional service starting Friday evening.

Trailing Fiona in the Caribbean is Tropical storm Ian, which is expected to become a hurricane on Sunday night. A hurricane watch is in effect for Cayman Islands.

The storms Ian's projected path takes it just south of Jamaica, over western Cuba and into Florida early next week, the hurricane centre said.

Florida Governor Ron DeSantis declared a state of emergency on Friday, freeing up funding and emergency services in advance of the storm.

Australian Associated Press