Police said two patrol cars were headed to back up another officer when they collided, then slammed into two other cars.
"One vehicle was heading northbound on Western, and the other one was heading westbound on James M. Wood," said LAPD Lt. Ron Katona.
A female sergeant was trapped in her car. She had to be extricated and is the one in critical condition.
"She's receiving evaluation as well as treatment for injuries that could be a broken pelvis and other injuries," said LAPD Asst. Chief Michel Moore.
A male officer has minor injuries, as does one of the drivers.
The other driver walked away with a sore knee.
"They're mandated by state law that if they have their lights and sirens on, that exempts them from some rules of the road, but they still have to proceed with caution and due diligence to make sure they're not putting themselves at risk or anybody in the public at risk," said Katona.
The crash is under investigation.