Hurricane Earl, which is churning towards Bermuda, is forecast to strengthen and bring dangerous surf and rip current conditions over the eastern US coastline later this week, forecasters have said.

Earl, the second of the 2022 Atlantic hurricane season, had maximum sustained winds of 100mph on Wednesday night, making it a category 2 storm.

It was expected to continue to strengthen and become a "major hurricane", a category 3, which has sustained winds of 111-129mph and can cause devastating damage.

"Although Earl's centre is forecast to pass southeast of Bermuda, tropical-storm-force winds are expected on the island this afternoon through early Friday morning," the US National Hurricane Center (NHC) said.

Hurricane-force winds are possible on Bermuda later today or tonight if Earl's track shifts farther west than is currently predicted, the Miami-based weather forecaster said.

"Swells generated by Earl are building near Bermuda and are expected to reach the US East Coast later today," the NHC added.

"These swells are likely to cause life-threatening surf and rip current conditions through the weekend."

A hurricane watch has been issued for Bermuda, a self-governing British overseas territory in the western North Atlantic Ocean.

The island's national security minister, Michael Weeks, told reporters that public services and government offices would keep operating but warned residents to brace for tropical storm conditions.

"Bermuda will certainly feel the effects from Earl, so we must guard against complacency," he said.

Farther east, Hurricane Danielle was slowly weakening over open waters about 605 miles north-northwest of the Azores. It had maximum sustained winds of 75mph.