Man kills himself in front of police after half-hour crime spree

Police have launched a critical incident investigation after a man's violent crime spree across several suburbs in Sydney's south, which ended when he killed himself.

An Australian man rammed his four-wheel-drive into a Sydney police car, hijacked a supermarket delivery truck and taxi, rammed other cars and stabbed and wounded a passerby before killing himself in front of police on Friday.

The dramatic chain of events, which police said was not terror-related, began around 3:00 pm when officers tried to stop a 4WD on the Hume Highway at Bass Hill because it wasn't displaying number plates.

The driver rammed the police car, dumped the four-wheel drive and hijacked a supermarket delivery truck about 7 km away, then continued across town for another 20 km to a suburb near the airport, hitting several cars along the way.

The driver, 24, tried to steal another car, stabbing a passerby who tried to stop him, before stealing a taxi. Police finally stopped the attacker in the taxi and tried to Taser him, but the man stabbed himself in the chest and died at the scene.

“The offender wasn’t trying to intentionally harm people,” Acting Assistant Commissioner Mick Fitzgerald told reporters in Sydney.

“It was a man who was attempting to do everything he could to avoid arrest. His actions, in particular, the actions when he stabbed the innocent person, (are) the actions of a person who we believe had mental health problems.”

Police did not identify the attacker or give further details. Fitzgerald said the man was known to police and did not have a significant criminal history.

The passerby who was stabbed was in a serious but stable condition in hospital, police said.

In November, a man set fire to a pickup truck laden with gas cylinders in Melbourne and stabbed three people, killing one, before being shot by police. Police described that rampage as an act of terrorism.