Four people died and 12 others were critically injured when two buses collided in a head-on crash in Seattle on Thursday. A charter bus and the popular Ride The Ducks of Seattle tour crashed on the Aurora Bridge. Seattle Fire Department Chief Harold Scroggins said fire crews responded at approximately 11:13 a.m. local time to a four-vehicle traffic accident. In addition to the buses, two other vehicles were part of the collision. Seattle Police Department Public Information Officer Lauren Lovanhill confirmed Thursday afternoon that the fatality count remained at four, while 12 passengers were still listed in critical condition and 32 others were being treated at various area hospitals with minor to serious injuries. It was not immediately clear what caused the crash. The National Transportation Safety Board confirmed it is looking into the incident. Seattle Fire Department Lt. Sue Stangl said earlier Thursday, when two people had been reported dead, that it was her understanding that the fatalities were on the charter bus, as were the majority of the critical injuries. She did not confirm the ages or genders of the passengers who were killed or injured. Melissa Mixon, the communications director for North Seattle College, said that approximately 45 students and employees with the NSC international program were traveling on the charter bus when it collided with the Ride The Ducks bus. "School starts on Monday, so this is usually a really happy time on campus,” Mixon added. “This is just incredibly sad." The international students on the charter bus were from “four or five different countries” whose consulates were being notified, Lovanhill said.