A bus carrying 29 people overturned on its side on Highway 101 southbound near Cesar Chavez in San Francisco according to fire officials.
Since the incident, which was first reported at 8:06 p.m., 23 victims have been transported to San Francisco General Hospital. According to San Francisco Fire officials, four people suffered serious injuries and 25 others endured minor to moderate injuries.
According to CHP officials, the driver lost control, sending the bus across traffic and sliding down the highway on its side. All passengers on board were injured.
"For some unknown reason that bus started to lose control, struck the center divider and then came back across the lanes and ended up on its side blocking the far right lane," said CHP officer Vu Williams.
Officials are still trying to determine why the driver lost control of the bus headed to a party on the Peninsula.
A Sig-alert has been activated. Only one lane on Highway 101 southbound is open, drivers can expect delays. Officials are asking drivers to avoid the area until further notice.
Check back for updates.