Burlington Northern Santa Fe spokesman Gus Melonas says Amtrak and Sound Transit commuter train passengers are taking buses while some freight trains can be rerouted through the Columbia River Gorge.
Melonas says repairs are under way. One of the three main-line parallel tracks should be open by 6 p.m. Wednesday and regular service should resume Thursday.
Melonas says the tracks were blocked before 6 o'clock Wednesday morning when two cars of a Union Pacific freight derailed as the train was switching to Burlington Northern Track just south of Seattle, near Boeing Field.
The two cars carrying general freight remained upright and there was no hazardous material spill. Cause of the derailment is still under investigation.
Sound Transit spokesman Lee Somerstein says about 1,500 passengers on three commuter trains were affected Wednesday morning. One was stopped at Tukwila and two others never left Tacoma.
Sound Transit is supplying some special buses Wednesday afternoon in Seattle for train commuters to Tacoma and others can take existing bus routes.
Somerstein says this is the first disruption in the Sounder Tacoma-Seattle run since service started in 2001.
Sound Transit service to Everett was not affected.