An earthquake with a preliminary magnitude of 7.7 off southern Chile has prompted a tsunami warning.

It struck 225km (140 miles) south-west of Puerto Montt in southern Chile, the United States Geological Survey (USGS) said.

The quake's depth was about 15km (10 miles).

Chile's national emergency office has issued an alert and ordered the evacuation of coastal areas of Los Lagos region.

"As a measure of precaution, we order the evacuation of coastal areas of Biobio, Araucania, Los Rios, Aysen," the alert said.

The Pacific Tsunami Warning Center said hazardous waves were possible on coasts located up to 1,000km from the quake's epicentre.

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