A Queensland cop who shot dead a man wielding a machete at the scene of a double murder was living "every police officers' worst nightmare".
The officer and another officer found the bodies of a man and a woman, both aged 43, after being called to a Coolum Beach property.
He shot the machete wielding man, 42, who later died in hospital. It is believed the homicide victims are a local couple and the alleged assailant was the man's brother, but police would not confirm it.
Queensland Police Union President Ian Leavers said the officer who used deadly force did what he had to do to protect his own life.
"Things unfolded extremely quickly," Mr Leavers told AAP.
"The police officer had no other option and in instances like this, you would only use a firearm to defend your life and we support the police officers involved." Mr Leavers described the officer as a well-respected family man who had more than 10 years experience in the service. Police Commissioner Ian Stewart said as the man was armed it seemed the officer had acted appropriately, but he would still be tormented by his actions.
"This is every police officers' worst nightmare," Mr Stewart said. "Every time they go to a call like this, they just don't know what they're going to confront. "My heart goes out for them for what they had to face."
Mr Stewart said the man died on the 10th anniversary of slain Caboolture cop Senior Sergeant Perry Irwin's death.
It made the events overnight even more poignant, particularly given they began in similar circumstances, he said.
The Ethical Standards Command has interviewed both officers. The coroner would also investigate. Yandina-Coolum Road, where the incident occurred, was closed for most of Thursday as police carried out their investigations.
Queensland Premier Campbell Newman said parliament's thoughts and prayers were with the family of the victims and the two officers involved.
