SEATTLE -- An unsecured load caused a multiple-vehicle collision that tangled up traffic for hours during Monday's evening commute on the Interstate 90 floating bridge, said Washington State Patrol Trooper Dan McDonald.

A chain reaction crash involving five vehicles and a semi-truck blocked two westbound lanes on I-90 at Midspan from about 3:40 p.m. to 6 p.m.

SLIDESHOW: Crash On I-90 Floating Bridge

McDonald said a car swerved to avoid a bucket on the freeway when the collision occurred.

More than 30 minutes after the collision, crews and medics were still working to remove drivers and passengers from the collision. In all, 6 people were transported to Harborview Medical Center; none of them have serious injuries.

A pickup involved in the collision spilled approximately 20 gallons of paint on the freeway and into a storm drain. The Department of Ecology is checking on the spilled paint.

Traffic backed up at least 6 miles to 148th Street Southeast in Bellevue.