CHP: charter bus driver not impaired during crash on SB Hwy 101 in San Francisco

At least 22 people were sent to the hospital Friday night after a charter bus overturned on U.S. Highway 101 in San Francisco, according to fire officials.

RELATED: Live traffic maps show back up from SF bus crash

Of the victims, four suffered serious injuries, nine suffered moderate injuries and 16 suffered minor injuries, San Francisco Fire Department officials said.

19 of those victims have now been released from the hospital, all victims are expected to make full recoveries.

The California Highway Patrol first reported the incident at 8:06 p.m. on southbound Highway 101 at the Cesar Chavez Street off-ramp.

The bus started wavering back and forth, hit the center median and bounced back across four lanes of traffic, crashing on the other side.

Most passengers were able to get out through broken windows or escape hatches. Two passengers had to be extracted by firefighters.

The overturned bus blocked southbound lanes and a Sig-alert was issued, closing all but one southbound lane.

The cause of the crash is still under investigation. Fire officials say the driver was not impaired.

"The driver, commend the driver. He had some injuries and he stayed on the scene and he was the very last person to get onto one of the ambulances. He wanted to make sure everybody was accounted for. Everybody's needs were taken care of and again he stayed here until everything was done and he was the last person to get onto a bus," said Lt. Jonathan Baxter, with the San Francisco Fire Department.

The bus is owned by Charter Brothers. It's a family-owned company that advertises more than 20-years of experience.

The company conducts charters for corporate events, schools, weddings and field trips.

The company's website says its buses can transport up to 56 passengers.

The crash was cleared around 2 a.m. this morning, according to the CHP.

Bay City News contributed to this report.