SEATTLE -- Traffic on southbound I-5 in Seattle backed up for miles Monday evening after state troopers shot and wounded a knife-wielding man.

Washington State Patrol says around 6:45 p.m. they received several 911 calls about a tan pickup truck swerving in and out of traffic in the middle of southbound I-5. The truck then stopped in the middle of I-5, blocking the two center lanes.

Two WSP troopers and a Department of Transportation vehicle responded to the scene after reports said the truck was on fire. While one trooper and the DOT tried to put out the truck fire, the other trooper headed towards the driver, who was about 20 feet away and spray painting a circle on the pavement.

WSP says when the suspect came at the trooper with a knife, the trooper tased the suspect. When nothing happened, the suspect was shot.

The Seattle Fire Department says medics rushed a man in his 20s to Harborview Medical Center where he passed away. The troopers were not injured.

Investigators said late Monday they had found an incendiary device inside the suspect's truck. It was described as a plastic bottle, roughly one liter in size with a cannon fuse sticking out of it.

RELATED: Check traffic

Monday evening a message board near 45th Street NEalerted drivers that all southbound lanesof I-5 wereclosed. In an adjacent neighborhood, plenty of traffic spectators said the backup was very bad.

Kristin Rowe watchedthechaotic scene for45 minutes.

I saw people getting out of their cars, said Rowe. I ve lived in Seattle a long time, and I have never seen that.

Greg Frethette was among the many passengers stuck on a bus for about an hour and a half.

They told us the highway is closed and it is a crime scene, and that we would have to stay put until the police department gave us permission to walk back, said Frethette.

Eventually some people were walking up the on ramp. Police turned some cars around on I-5 too.

Driver Kirsten Johnson was grateful to get out of the gridlock.

I'm trying to get to the airport because my dad is in the hospital, said Johnson.

Just glad to get moving, seriously, said a detoured driver.

KING 5's John Langeler, Natalie Swaby and Liza Javier contributed to this report.

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