A “duck boat” tour vehicle and a charter bus carrying foreign college students collided on a busy Seattle bridge Thursday, killing four people and sending dozens to hospitals.

The Seattle Times reported that all four killed were students at North Seattle College. The Times interviewed Ron Chow, a representative of the Chinese consulate, who said that 48 students from six countries were involved in the collision. He wasn’t sure how many of them are Chinese, the Times reported.

The collision happened on the Aurora Avenue bridge, which carries one of the city’s main north-south highways over a lake.

At least 12 people were in critical condition, and many others suffered minor injuries, Fire Chief Harold Scoggins said.

What we know: http://t.co/D2hBcVIkpS #AuroraBridgeCrash pic.twitter.com/zc4AC21XNC

— The Seattle Times (@seattletimes) September 24, 2015

There was no immediate word about the cause of the crash, which involved a military-style tour bus that can also be operated on water. Initial reports described the accident as a head-on collision.

A driver who was behind the duck boat said the tour bus and duck boat were headed in opposite directions.

Brad Volm, 23, of Philadelphia, said the amphibious vehicle swerved in front of him. The left front tire of the duck boat appeared to lock up, and then the vehicle swerved into the oncoming charter bus, Volm said.

Witnesses described hearing a loud screech and then seeing injured people lying on the pavement or wandering around in a daze.

Jahna Dyer, a registered nurse, said she was walking across the bridge when she came upon the scene, a mess of jumbled metal and glass. Some victims were lying on the road. Others milled about, seemingly in shock and falling down.

Dyer jumped a railing separating the sidewalk from the roadway and helped stabilize an injured man’s neck. She said she also helped a woman who had a cut lip and glass in her eye.

“She was holding my hand and saying thank you,” she said.

John Mundell said he was at the south end of the bridge when the crash occurred.

“We could hear the screech and twisted metal. It was surreal,” he said, adding he saw what appeared to be a few dozen people on the ground. “I wanted to try to help. I felt helpless.”

When emergency crews arrived, “a lot of people were running at them,” pleading for help, Seattle Fire Lt. Sue Stangl said.

The amphibious vehicle is operated by a tour company called Ride the Ducks, which offers tours that are known for exuberant drivers and guides who play loud music and quack through speakers as they lead tourists around the city.

Company President Brian Tracey called the fatal accident “devastating” and told The Seattle Times that the company continually trains and conducts ongoing education classes to ensure safety.

Mayor Ed Murray said foreign students were on the charter bus, and efforts were being made to contact consulates. He had no other details.

The bridge was expected to be closed for hours. It has three lanes in each direction and no barrier separating the north and southbound lanes.

The safety of the amphibious boats has been questioned before. Lawyer Steve Bulzomi represented a motorcyclist who was run over and dragged by a Ride the Ducks boat that came up behind him at a stoplight in downtown Seattle in 2011.

“These are military craft that were never designed to navigate narrow city streets,” Bulzomi said Thursday. “This is a business model that requires the driver to be a driver, tour guide and entertainer at the same time. It asks too much of the driver.”

In 2010, a barge plowed into an amphibious vessel packed with tourists that had stalled in the Delaware River in Philadelphia.

The crash sent all 37 people on the duck boat into the river, but 16-year-old Dora Schwendtner and 20-year-old Szabolcs Prem never resurfaced. The Hungarians were visiting the United States through a church exchange program. Their families filed wrongful-death lawsuits.

A tug operator, Matt Devlin, eventually pleaded guilty to involuntary manslaughter in the crash. Devlin acknowledged the accident was caused largely by his continuous use of a cellphone and laptop computer while he was steering the barge.

In July, the family of a woman struck and killed by an amphibious tourist boat in Philadelphia filed a wrongful-death lawsuit.

Attorneys for Elizabeth Karnicki’s family allege the May 8 accident, which occurred during rush hour, was due in part to “huge blind spots” on the Ride The Ducks vehicle.

Story by the Associated Press