An Amtrak train derailed south of Seattle, and authorities say "injuries and casualties" were reported.

The train derailed about 40 miles south of Seattle before 8 a.m. Monday, spilling at least one train car onto busy Interstate 5.

The Pierce County Sheriff's office says in a tweet that the train was heading south and that there were "injuries and casualties," but no numbers were immediately available.

All southbound lanes of Interstate 5 were closed south of Joint Base Lewis-McChord, and motorists were being warned to avoid the area.