A police officer was seen chasing a suspect and grappling with him on the roadside in California.

Footage shows an Ontario Police Department officer approaching an accused who was backing away from him.

However, the cop turned offensive when the resident refused to submit and went into a fighting stance.

The pair squared off until the policeman caught the alleged offender in an arm lock on May 8

However, the officer was seen continuously beating the man, who was significantly smaller than him, even when he was already down on the pavement.

He was seen punching the suspect's head and face while commanding him to surrender his hands.

The cop only stopped when his colleague arrived to help him handcuff him.

Passing driver Kenneth Payton, who was parked on the other side of the road when the arrest happened, said it was 'clearly an excessive use of force'.

He said: 'In Ontario, California, I witnessed clearly excessive use of force by the Ontario Police Department.

'This incident occurred on the cross streets of Grove Avenue and Holt Boulevard.'