Authorities in the US Washington state say four people have been killed during a shooting at a mall north of Seattle and at least one suspect remains at large.

The Washington State Patrol says on Twitter the four were shot Friday at the Cascade Mall in Burlington, about 105km north of Seattle.

Sgt Mark Francis says authorities are searching for a man wearing grey who was last seen walking towards a highway from the mall. Francis says it wasn't immediately known if there was more than one gunman involved.

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