Official US landslide toll rises to 21

The confirmed death toll from a US landslide has risen from 18 to 21, while four more bodies have been found but not counted in the official tally, authorities say.

Fifteen of the victims of the mudslide in Washington state have been formally identified, said Snohomish County Emergency Management Department program manager Jason Biermann.

Thirty people remain missing after a rain-soaked wall of mud, trees and debris crashed down onto the edge of the town of Oso on March 22.

A total of 49 dwellings in the rural town were hit by the rush of mud, rocks and trees, which also destroyed part of a highway about 95km northeast of Seattle.

Hundreds of rescue workers have been working in tough conditions for seven days. A few survivors were found immediately after the mudslide, but none since the day of the catastrophe.