About three hours after the earthquake, US authorities warned that "minor sea level fluctuations" of up to 30cm (11.8 inches) could still occur, but that any serious threat had passed.

The USGS said large earthquakes at this location of the plate boundary are not unexpected.

In 2018 a 7.5-magnitude earthquake occurred nearby, causing some damage and a small tsunami, it said.

"Luckily, the remote location of these earthquakes limits the potential for significant damage due to shaking," it added.

Separately, the US National Tsunami Warning Centre said there are no alerts for the mainland US coast.