The number of people missing in a deadly Washington state landslide has fallen from 90 to 30 after many people on the official missing list were confirmed alive.

However, the confirmed death toll in last week's disaster in Oso, north of Seattle, rose by one to 18 with the confirmation of the identity of another victim on Saturday. 

Another body has yet to be identified, and the presumed final death toll will be 28, according to authorities.  

Officials previously said they expected the missing figure to drop as they found people and cross-referenced a list that included partial reports and duplicates.

The massive landslide struck Oso on March 22, sweeping away 49 homes and destroying part of a highway.

Some survivors were rescued immediately after, but none has been found since last Saturday.

Jason Biermann, an emergency services spokesman, said the task of counting the dead was complicated by the state of human remains left by the landslide. "Often they are making partial recoveries," he said.

Source: Agencies