Police were tracking the minivan about 1:20 p.m. in the parking lot of a Best Western motel in the 5700 block of La Palma Avenue when the pursuit began, said police Sgt. Daron Wyatt.
The suspect "intentionally rammed an undercover police car, then maneuvered his way around towards a marked unit," the sergeant said. The driver jumped out of the minivan while it was still in gear; it then crashed into the second police vehicle.
No officers were injured.
The man fled on foot into the Santa Ana riverbed, near the 91 Freeway, police said. Five other occupants of the stolen vehicle - four women and one man - were detained, and a loaded handgun was recovered.
UPDATE: Extensive search still underway with helo, K9, and officers on the ground searching tunnels under the riverbed and freeway pic.twitter.com/OMgGo8WGOF— Anaheim PD (@AnaheimPD) February 9, 2017
The driver swam across the riverbed before making his way into a tunnel under the freeway. A massive search effort ensued, assisted by K-9 units and a police helicopter, but the suspect had not been found by 4 p.m.
He is described as being in his 20s, with a thin build. His red T-shirt and other clothing were wet from crossing the riverbed, authorities said.
Anyone with information about the wanted man's whereabouts is asked to call 911.