UPDATE as of 6:50 p.m.
WSDOT reports that all lanes are clear.
UPDATE as of 5:55 p.m.
State Trooper Guy Gill said the backup on southbound I-5 at Gravelly Lake Drive is caused by three separate collisions involving eight vehicles, including a jack-knifed semi-truck.
Some of the drivers suffered minor injuries.
A cement truck is also on its side in the northbound I-5 lanes just south of state Route 512, Gill said.
Although the truck is not blocking lanes, drivers are slowing down to look at the accident.
Traffic in the southbound lanes is backed up to SR 512 but drivers are getting by in the right lane.
A collision involving a semi-truck and two vehicles is blocking the three left lanes of southbound Interstate 5 at Gravelly Lake Drive near Lakewood, according to the state Department of Transportation.
The collision occurred at 5:20 p.m. and traffic is backed up to state Route 512.