Six people, including two police officers, were shot and killed in an exchange of fire at a remote property in Australia's Queensland state, authorities said on Tuesday.
The shootings happened after police visited the place to investigate reports of a missing person.
Officers were shot by two armed offenders on Monday evening when they approached the residence on the property in Wieambilla, about 300km north-west of Queensland's capital Brisbane, state police.
After specialist officers and air support responded to a siege situation at the property, three offenders, including a woman, were shot dead, police said.
A member of the public was also killed while two other police officers were taken to the hospital with non-life-threatening wounds.
Gun crime in Australia remains relatively rare, with some of the world's toughest gun laws introduced after a lone gunman killed 35 people in April 1996 at a cafe and tourist site at the former colonial prison of Port Arthur on the island state of Tasmania.
The officers visited the property after a missing person's report was filed in New South Wales for Nathaniel Train, media reported.
Mr Train, 46, a former school principal in New South Wales, his brother Gareth Train and an unidentified woman were the attackers shot dead by the police, they also reported.
The police have not formally revealed the identities of the armed offenders.
The police officers who were killed were Constable Matthew Arnold, 26, and Constable Rachel McCrow, 29, police said.
Prime Minister Anthony Albanese described the incident as “terrible and a heartbreaking day for the families and friends of the Queensland Police officers who have lost their lives in the line of duty”.
“My condolences to all who are grieving tonight — Australia mourns with you,” Mr Albanese said in a tweet.
Queensland Police Commissioner Katarina Carroll said the shooting was the largest loss of life the state police had suffered in one incident in recent times.
Circumstances surrounding the incident, including the deaths, will be investigated, Ms Carroll said.