SAN FRANCISCO, Dec. 18 (Xinhua) -- At least three people were killed and more than 100 others injured Monday when a train run by intercity rail operator Amtrak derailed on its first run along a new route in Pierce County in the U.S. state of Washington, local media reported.

The Amtrak 501, carrying 77 passengers and six crew members, was heading south from Seattle when 13 of its 14 cars jumped tracks near Tacoma, a city in Pierce on the West Coast, with some cars falling off a bridge.

The train was making its first run along a new route with the tracks first put to public use after weeks of inspection and testing, the county sheriff's department said.

The tracks, known as the Point Defiance Bypass, are owned by Sound Transit, a public transit agency serving the Seattle metropolitan area in Washington.

TV footage showed several cars fell off a bridge over a traffic-clogged highway.

The sheriff's department said earlier Monday that some motor vehicles and two semi trucks were hit on the freeway below, but no motorist fatalities were reported.

An investigation was ordered even as rescuers were trying to remove the overturned cars.

The U.S. National Transportation Safety Board said a 20-member team of investigators will arrive at the scene.

President Donald Trump offered his "thoughts and prayers" for the accident victims.

The National Railroad Passenger Corporation, or Amtrack, said its service south of Seattle has been suspended but the service from Seattle to points north and east continued.

Founded in 1971 and headquartered in the Union Station in Washington, D.C., Amtrak is a passenger railroad service that provides medium- and long-distance intercity service.

It serves more than 500 destinations in 46 states and three Canadian provinces with more than 300 trains running over 34,000 km daily.