The vans were driving south side by side on U.S. 101 near Bradley in Monterey County when they crashed into each other around 12:30 p.m., Officer Joel Newby said.
The collision sent one van into the center divide, where it rolled over. Two students were ejected through a broken window. The CHP initially said the two students were seriously injured but later described their injuries as moderate.
The two students were taken by helicopter to trauma centers. Two other students were taken by ambulance to local hospitals, also suffering from moderate injuries.
The remaining injured students suffered minor injuries that didn't require medical treatment, the CHP said.
The students, undergraduates from the university's Foster School of Business, belonged to an organization that connects American students with internships abroad, as well as foreign students with internships in the U.S., university spokesman Bob Roseth said. In all, there were three vans transporting 33 Washington students to the organization's regional conference in Santa Maria.
A stunned group of survivors gathered outside the hospital where some of their classmates were taken.
Hanne Ockert-Axelsson, who was driving one of the vans, said she was shocked and traumatized by the crash.
"We were driving on a straight road that seemed to turn parallel almost and one of the cars hit the back of the other car which made it swerve," she said.
Despite the scary accident, Ockert-Axelsson said many of her classmates still want to attend the conference.
"Hopefully a majority of the members still can attend the conference because we do want people to get back on the horse," she said.
By late Friday night, only two of the students were still in the hospital.
The cause of the accident was under investigation.