Ernesto restrengthened into a hurricane on Sunday as it travelled well off the shore of eastern United States, threatening wind and rain along the US and Canadian coasts after pummelling Puerto Rico and Bermuda.

The hurricane, whose centre is forecast to pass near southeastern Newfoundland, Canada late on Monday into Tuesday, was creating dangerous conditions for residents and vacationers along the North American Atlantic seaboard, the US National Hurricane Center said.

"Beach goers should be aware that there is a significant risk of life-threatening surf and rip currents, and should stay out of the water if advised by lifeguards," the NHC said.

Ernesto brushed past Puerto Rico earlier in the week leaving more than 600,000 customers without power, then hit Bermuda directly on Saturday, causing more than 70 percent of customers to lose electricity.

Michael Weeks, Bermuda's minister of national security, reported on Sunday that the island "made it through Hurricane Ernesto without any injuries or major incidents," according to The Royal Gazette newspaper.

Packing maximum sustained winds of 120 kilometres per hour, Ernesto was a Category 1 storm on the five-level Saffir-Simpson scale as of the NHC's latest advisory at 5:00 pm (2100 GMT) on Sunday, with some increase in speed expected overnight.

Swells from Ernesto are affecting parts of the Bahamas, Bermuda, the US East Coast and Atlantic Canada, the NHC said.

There were no coastal watches or warnings in effect, with the storm located some 520 miles south of Halifax in Canada.

Warmer-than-normal Atlantic waters threaten to supercharge this year's hurricane season, scientists have warned.

Scientists say climate change likely plays a role in the rapid intensification of storms because there is more energy in a warmer ocean for them to feed on. (AFP)