A vehicle that struck 22 Los Angeles County sheriff’s recruits on a training run around dawn Wednesday, critically injuring at least five of them, was travelling on the wrong side of the road just before the crash, authorities said.

A total of 23 people were injured, including the driver, said Los Angeles County Fire Department spokeswoman Captain Sheila Kelliher.

“I am personally heart sick,” Los Angeles County Supervisor Janice Hahn said, adding that she was focusing on the cadets who were injured to pull through this.

The crash occurred just before 6.30am in suburban Whittier, where a training academy is located.

California Highway Patrol Assistant Chief Charlie Sampson said about 75 recruits were running in formation northbound in the street when the southbound vehicle veered into the opposing lane and struck the victims.

Sampson identified the driver as a 22-year-old man from suburban Diamond Bar but withheld his name.

Police gather at a scene where an SUV struck Los Angeles County sheriff's recruits in Whittier, California. Photo / AP

Sampson said the driver was cooperating with investigators. All possibilities, ranging from an intentional act to impaired driving, will be investigated, he said. Sampson said he did not have the results of a failed sobriety test.

TV news helicopter broadcasts showed a significant response of firefighters and ambulances, an SUV with severe front-end damage straddling a toppled pole on a sidewalk, as well as numerous individuals nearby in uniform workout clothes. There was also a 40km/h speed limit sign.

Running shoes and a backpack were strewn around the scene.

“Our hearts are with the Los Angeles County Sheriff’s recruits injured this morning while training to serve their communities,” California Governor Gavin Newsom said in a statement. “Jennifer and I send our best wishes for their recovery and stand with their loved ones and colleagues at the Los Angeles County Sheriff’s Department during this difficult time.”