Firefighters used ladders to reach into the bus' windows to pull out victims. They used chainsaws to gain entry into the front of the bus, The Desert Sun reported.
Photos show the front of the bus pushed into the semi-truck's trailer.
"The intrusion into the bus compartment is significant," Hamilton said.
The bus, identified as a USA Holiday bus, crashed into the big rig's trailer. USA Holiday is known for transporting people from Los Angeles to Southern California casinos, according to The Desert Sun.
Tow trucks attempted to lift the bus from the semi and to pull the semi forward, away from the bus.
"The whole front of the bus up to about the second or third row of seats was completely crushed into the left rear side of the semi truck," a witness told The Desert Sun. "By the time I got there, there were at least a dozen firefighters climbing into the passenger bus, pulling people out."
The driver of the big rig was not injured, KWWL reported.
Rich Ramhoff, director of marketing at Desert Regional Medical Center, said that of the 14 patients the hospital received, five victims are in critical condition, three are in serious condition and six had minor injuries. He told The Desert Sun that in his six years at the hospital, this was the largest number of victims he'd seen from a single incident.
Lee Rice, of the Eisenhower Medical Center, said that the Rancho Mirage hospital received 11 adult patients, all with minor injuries.
Victims were also transported to John F. Kennedy Hospital in Indio, California.
The California Highway Patrol said all westbound lanes of the highway are closed and traffic is being diverted. CHP officials estimate the freeway could be closed until 4 p.m.