Two students and a driver remained hospitalized Friday morning after a school bus crashed into a tree in Anaheim Hills, and authorities were continuing to investigate what caused the bus to veer off the road, apparently without braking.

The bus, carrying 11 middle school students, went airborne then down a hill before coming to a stop against a eucalyptus tree on northbound Nohl Ranch Canyon Road (map) Thursday afternoon, witnesses said at the time.

The Orange Unified School District bus was being driven by Gerald Douglass Rupple II, who had to be extricated from the front of the vehicle, authorities said.

Two students and 24-year-old Rupple were critically injured, while three other students were hospitalized for minor injuries.

The three who were critically injured remained hospitalized Friday. A hospital spokeswoman said the two students were “awake and alert” at Western Medical Center in Santa Ana.

Rupple was recovering at UCI Medical Center in Irvine, and his father said he would spend another night at the hospital.

The bus had been traveling at an “unknown speed” when the vehicle veered to the right and up a dirt embankment, according to a California Highway Patrol news release sent out Friday morning. The bus struck a tree and was seriously damaged, the release stated.

It was not known why the bus veered off the road, CHP stated in the release.

“There were no skid marks on the roadway,” CHP Officer Florentino Olivera said Friday.

“With there not being any skid marks, it’s hard to determine if he applied the brakes or not,” he said. “If he did, did the brakes work properly? So that’s why we’re going to inspect the bus.”

Video cameras were on the bus and Olivera said the recordings would be examined Monday.

The bus had passed an inspection in October 2013, authorities said.

The vehicle had been removed from the scene by early Friday, authorities said.

One witness said the bus had been traveling at 70 mph before the crash, but that had not yet been confirmed by CHP, Olivera said.

“Almost a 100 percent sure that bus driver passed out before this accident happened,” said Taylor Fabozzi, who described the bus veering into his lane, narrowly missing his own vehicle just prior to the crash.

Rupple did not appear to be moving as the crash occurred, according to student Jordan Gray, who was on the bus.

“I heard all this crashing next to me and I was freaking out … I started calling my bus driver’s name,” Gray said. “He wasn’t moving at all.”

Student Solymar Colling, also a passenger, said she immediately tried to find her phone to call for help once the bus stopped.

“We started driving down the hill,” Colling said. “It went sideways and I heard a lot of thumps and stuff from people hitting things.”

There were seatbelts on the bus, but it was not known if the students were wearing them, according to CHP officials.

Rupple had a broken clavicle and required stitches above both eyes, his mother told KTLA on Thursday.

He has worked full time for the district since October 2010, Orange Unified stated.

KTLA’s Melissa Pamer, Sara Welch and Mary Beth McDade contributed to this report.