A National Transportation Safety Board team is en route to Seattle to investigate Thursday’s deadly collision involving a “Ride the Ducks” tour vehicle and a charter bus, the agency announced Friday.

Four international North Seattle College students on a new school orientation trip died in the accident on Aurora Bridge, according to the school. Authorities have not released their identities as families are still being notified.

Another 47 people were injured in the collision and transported to local hospitals. As of Thursday night, two remained in critical condition at Harborview Medical Center.

“No words are adequate to express the absolute pain and sorrow we all feel as a result of receiving this devastating news,” reads a statement from North Seattle College.

The head-on crash at 11:11 a.m. Thursday involved an amphibious tour vehicle, a bus and several cars, according to the Seattle Fire Department. About 50 people at the scene were evaluated for injuries.

“Seattle had a terrible tragedy today. There has been loss of life and dozens of injuries,” Seattle Mayor Ed Murray said Thursday.

Two buses were carrying North Seattle College students and employees to Safeco Field for an event tied to new student orientation, when one of the buses carrying about 45 people collided with the duck boat vehicle, according to the school.

“It was to be a fun introduction to Seattle,” school spokeswoman Melissa Mixon told the Associated Press.

Ride the Ducks Seattle will suspend operations until Monday “out of respect for the people who have lost their lives and those who are injured,” reads a company statement.

“Ride the Ducks also again wishes to express its deepest condolences to all of the victims, and their families and friends,” reads the statement.

About 90 firefighters and medics swarmed the bridge over Lake Union, according to the fire department.

Bloodworks Northwest made a public appeal for blood donations to help those injured in the crash.

Eyewitnesses told various media outlets that the duck vehicle had collided with the bus, but as the Associated Press reported, authorities haven’t announced the cause of the crash.

“The scene was pretty gruesome,” Jesse Christenson, who witnessed the crash, told the Seattle Times. “There were people in shock.”

From the AP:

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

A passenger aboard the Ride the Ducks vehicle told the Seattle Times he was standing in the aisle and had just snapped a photo of Lake Union when “just at that moment, I heard the driver go: ‘Oh no!'”

Tim Gesner told the paper he then saw the duck boat heading into oncoming traffic and into the side of a bus. He was thrown into the air.

“It was like I was in slow motion, bouncing off things and just feeling the pain shooting everywhere,” he said. After landing, “I turned and looked, and that’s when I saw the carnage.”

The amphibious vehicles are known for giving silly, entertainment-focused tours of Seattle on land and on water. Captains hold Merchant Mariner Master’s licenses and commercial driver’s licenses, according to Ride the Ducks.

Some have previously questioned the safety of the duck boat vehicles, particularly given that drivers also act as tour guides. In 2011, a vehicle slammed into a motorcyclist in Seattle in a case the company settled out of court.

Ride the Ducks Seattle has independently operated in the city since 1997. “The Department of Transportation and Coast Guard inspect our vehicles annually,” the company said. “Safety is our company’s highest priority.”

The bus company is run by Bellair. President Richard Johnson told KOMO that the company has a good safety record.

“You’ve got to take your responsibility very seriously when you’re carrying all the passengers we do in a year,” he said.

[This post, first published Sept. 24, has been updated.]