The Ethical Standards Command is investigating the death in custody of an Aboriginal man in the Queensland city of Toowoomba on Thursday.
The 27-year old man died during a "violent struggle" with police that also left two officers with minor injuries.
Assistant Commissioner Mike Condon told reporters that officers were called to Stone Street, Wilsonton, in response to a report about a man allegedly trying to steal a car.
“Police attempted to detain the occupants of the vehicle... during an altercation with police a 27 year-old male person became unconscious,” he said.
“Police immediately provided first aid, QAS officers attended shortly after, and continued to provide first aid, and sadly that 27-year old male person has passed away.”
He would not comment on how the man became unconscious.
The investigation will be undertaken with oversight by the state coroner and the Crime and Corruption Commission.
“The mere fact it was involved in an altercation will necessitate that we investigate the use of force used by our officers,” Mr Condon said.
One of the police officers involved experienced breathing difficulties, and the other had minor injuries.
They are yet to be interviewed, but Mr Condon said that was likely to happen within 24 hours.
"The normal process is that they will stand down for a couple of days to regather themselves, but it really depends on the individual. But we are here to support them."
Anyone with mobile or CCTV footage of the tragic incident is being urged to come forward.