Earthquake in Alaska: Tsunami warning after enormous 7.8m tremor strikes off coast

A 7.8-magnitude earthquake has struck off the coast of Alaska - putting nearby coastal settlements at risk of a tsunami.

The shallow six-mile wide quake started at 6.12am GMT on Wednesday, or 11.25pm PST on Tuesday.

It was felt as far away as Anchorage, a distance of 500 miles, and hit around 60 miles south-southeast of the remote settlement of Perryville, according to the US Geological Survey. 

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The shallow six-mile wide quake started at 6.12am GMT on Wednesday, or 11.25pm on Wednesday PST, on Wednesday

The earthquake had a depth of six miles. 

A distance of 200 miles surrounding the epicentre of the quake has been put on the watch for a tsunami - which is a large wave of water triggered by the dramatic shifting of tectonic plates during an earthquake. 

At risk areas include Amchitka Pass, Samalga Pass, Kennedy Entrance and Cape Suckling. 

Aftershocks are expected to continue over the next week. 

A spokesman for USGS, which measures the risk, said: 'The USGS advises everyone to be aware of the possibility of aftershocks, especially when in or around vulnerable structures such as unreinforced masonry buildings.

'This earthquake could be part of a sequence. An earthquake sequence may have larger and potentially damaging earthquakes in the future, so remember to: Drop, Cover, and Hold on.' 

The body forecast a four per cent chance of another earthquake even larger than 7.8 magnitude. 

More to follow.