A man allegedly wielding a knife has been shot by police after he was involved in a traffic crash at Oxley in Brisbane's south-west, Queensland police say.

Key points: Police allege the man was initially involved in a carjacking at Darra

Police allege the man was initially involved in a carjacking at Darra The alleged offender was shot in the torso at Oxley

The alleged offender was shot in the torso at Oxley Police are calling for any witnesses to contact them

Detective Superintendent Tony Fleming said the man had been taken to hospital in a "very serious" condition.

He said the man was allegedly involved in a carjacking at Darra.

The man then allegedly drove the stolen vehicle along Seventeen Mile Rocks Road towards Station Road in Oxley.

Detective Superintendent Fleming said the man had crashed the stolen car into the rear of another car going slowly through an intersection.

He said the man then allegedly got out of the stolen vehicle with a knife and attempted to steal a second car.

Detective Superintendent Fleming said a 20-year-old man tried to help a woman in the second car but was struck by that vehicle and taken to hospital.

The man has been taken to hospital in a very serious condition. ( ABC News )

He said the alleged offender tried to steal a third vehicle and then ran down the road holding a knife.

A police officer who was driving along Station Road spoke to the man in a nearby park.

Detective Superintendent Fleming said the officer discharged a taser at the man, which was "unsuccessful".

"[The officer] was then threatened with a knife, where he feared for his safety, and he discharged a number of rounds from [his] pistol," Detective Superintendent Fleming said.

"The man was struck a couple of times in the torso."

He said an ambulance was called and the man was taken to hospital.

Detective Superintendent Fleming said the man was known to police.

Police are calling for any witnesses to come forward as the investigation continues.