September 27, 2015 update at bottom of story.

Four college-aged Chinese exchange students were killed Thursday on Seattle’s Aurora Bridge when the charter bus in which they were riding collided with an amphibious Ride the Ducks tour vehicle and two smaller vehicles.

The accident left 15 people in critical condition and 17 in serious condition, according to King 5 News.

At least 51 people reportedly were evacuated from the scene and taken to eight different hospitals in the Seattle area. The Harborview Medical Center told USA Today their ages range from a 17-year-old girl to a 61-year-old man.

Harborview officials said the center was still trying to identify three patients. who either had no identification and were unconscious or who did not speak English.

Seattle Mayor Ed Murray said traffic was being diverted to the Ballard and Fremont bridges while the Aurora Bridge would be closed for investigators, possibly until Friday.

The charter bus was carrying 45 international students and staff from North Seattle College to Safeco Field as part of student orientation. The collision occurred around 11:15 a.m. PT when the amphibious vehicle and the bus collided, ripping out the side of the bus, a witness told The Seattle Times.

Seattle Fire Chief Harold Scoggins told the New York Daily News that 90 firefighters, 11 fire engines, seven ladders and eight paramedic units responded to the scene.

Ride The Ducks, which operates amphibious, military-style vehicles, is known for its tour rides throughout Seattle. During tours, drivers and guides often play loud music and quack through megaphones. According to the company web site, the vehicles do not have seat belts.

Following the accident, Ride The Ducks announced it is suspending all operations.

The Utilities and Transportation Commission, which regulates Bellair Charters and Ride The Ducks of Seattle LLC, said it would be inspecting all vehicle and driver records related to the crash to determine if both companies complied with state and federal guidelines, according to King 5 News.

Update Sept. 27, 2015: According to Komo-TV News, a 20-year-old woman died on Sunday Sept. 27, after being injured in the crash between a charter bus and Ride The Ducks tour vehicle.

Additionally, there was a demand for O-positive and O-negative blood types due to over 40 people with injuries. Bloodworks Northwest issued an urgent appeal to blood donors who have not donated recently to visit one of their 12 centers or mobile drives, according to Kent Reporter.