UPDATE 4:50 PM: After confusion about casualty numbers, the Washington State Patrol now says three people have been confirmed dead. Original post below:

An Amtrak train has derailed on a bridge over Interstate 5 in Pierce County, reportedly killing several passengers. Media reports earlier this morning said three people were dead. The Associated Press then reported six people dead, citing an unnamed official who was briefed on the investigation. That official also said the train "may have struck something on the track" before derailing, the AP reports.

The Pierce County Sheriff's Office says it has not released any numbers about how many people have died:

The Washington State Patrol has also not released numbers. The southbound train derailed near Mounts Road, which is about 13 miles north of Olympia, according to state and county officials.

In total, 13 cars derailed. Five vehicles and two semi trucks were hit on the freeway below, according to the Washington State Patrol. Motorists on the freeway were injured but not killed, according to the Sheriff's Office.

According to Amtrak, 78 passengers and five crew members were on board the train. A total of 77 patients were being transported to hospitals in Pierce and Thurston Counties, four of them considered “level red” with the most severe injuries, according to a spokesperson for CHI Franciscan Health. Patients will be treated at St. Joseph’s in Tacoma, Tacoma General Hospital, St. Claire’s in Lakewood, and St. Anthony’s in Gig Harbor, according to the spokesperson.

Washington State Patrol and emergency medical responders are at the scene. Southbound lanes of the interstate are closed. After completing the emergency response and allowing the National Transportation Safety Board to review the scene, crews will remove the train from the interstate, according to the Washington State Department of Transportation.

Train 501 was in its first morning of service on a new route running parallel to I-5. The train left Tacoma "moments before the accident," according to The News Tribune. Sound Transit owns the tracks on the route, known as the Point Defiance Bypass, according to WSDOT. Sound Transit recently upgraded the tracks with the help of federal funding. Amtrak says service south of Seattle is temporarily suspended.

Chris Karnes, chair of Pierce Transit's Community Transportation Advisory Group, was tweeting from the train about the new service. "The train has derailed. Emergency crews are on the scene," he wrote at 8:01 am. "Massive damage. People are hurt."

"It sounded like being on the inside of an aluminum can being crushed," Karnes told the Seattle Times. "And then we were not on the tracks anymore."

Governor Jay Inslee has declared a state of emergency due to the derailment. In a statement, Inslee said, "Today’s tragic incident in Pierce County is a serious and ongoing emergency. Trudi and I are holding in our hearts everyone on board, and are praying for the many injured."

In a statement, Seattle Mayor Jenny Durkan called the derailment "horrific."

"My thoughts are with the passengers, families and those injured as well as our first responders, firefighters and police who rushed to the scene," Durkan said. "The City of Seattle has offered our assistance and aid to Pierce and Thurston counties, and is ready to work with Amtrak, local, state, and federal officials as they manage the response and deal with the aftermath of this tragic incident."

President Donald Trump used the accident to call for new infrastructure, despite this being a newly opened line that was part of a $181 million project.

This summer, another Amtrak train derailed near Tacoma, with only minor injuries reported. Worth noting: 2010 statistics from the federal Department of Transportation show that highway-related injuries (including cars and motorcycles) outnumbered railroad-related injuries (including Amtrak) more than 300 to one.

We're updating this post with more information as it becomes available.