The fatal shooting of two young police constables killed in an ambush on a remote Australian property has been described as a "ruthless and cold-blooded execution".
Constables Matthew Arnold, 26, and Rachel McCrow, 29, died along with 58-year-old neighbour Alan Dare after being shot at Wieambilla in the Western Downs region on Monday.
Three alleged killers – a former NSW school teacher, his brother and sister-in-law – died in a firefight with heavily armed tactical officers later in the evening.
Four police officers went to the Wieambilla property to look for missing NSW man Gareth Train at 4.30pm on Monday after being asked by police in that state.
The 47-year-old, his brother Nathaniel Train, 46, and his 45-year-old sister-in-law Stacey Train opened fire on the officers after they jumped a fence.
A "hail of bullets" struck constables Arnold and McCrow, who fell to the ground, with 28-year-old constables Keeley Brough and Randall Kirk taking cover before escaping.
The three Trains then walked up to constables Arnold and McCrow and shot them both at point-blank range while they lay on the ground.
The two other officers were taken to hospital with non-life-threatening injuries.
Neighbour Alan Dare was also shot and killed by the armed offenders.
The exclusion zone set up by Queensland Police following the fatal shooting of two officers at Wieambilla. – AAP
An emotional police commissioner Katarina Carroll said the officers "never stood a chance".
"The fact that two got out alive is a miracle," the commissioner said. "To think they survived the scene, let alone ... called for assistance, is just extraordinary."
Police union boss Ian Leavers said the officers were executed.
"The ruthless, murderous trio have then gone and executed the two police, our fallen officers, who were on the ground. They have executed them in cold blood," he said.
The shooters then lit a fire to burn or smoke Constable Brough out of her hiding place in the long grass and into the open.
Mr Leavers said the officer, who had only eight or nine weeks of experience, believed she was going to be shot dead or burnt alive.
"I do know she was sending messages to loved ones saying she almost was at a point where she thought it was her time," he said.
Tributes are left outside the police station in Tara. – AAP
Mr Dare, who had come out of his property to check on the grassfire, was also shot in the back by the trio "in cold blood as well" and died.
Sixteen police officers then tried to rescue their colleagues, but were met with heavy gunfire and had to retreat.
Specialist police were called in, as were police helicopters, which the trio also fired at, before they were killed in a gunfight about 10.30pm, local time.
Social media posts have linked Gareth Train to an online conspiracy community, and sources have told AAP that Nathaniel had been living "off the grid" for more than 12 months.
A siege situation ensued, with specialist police and PolAir responding, before coming to a bloody final end hours later.
"Two males and a female were fatally shot during a confrontation with police shortly after 10.30pm," the force said in a statement.
The alleged killers have been identified by senior police sources as Nathaniel Train, his brother Gareth and his wife Stacey.
All three are considered to have been offenders actively involved in the ambush that unfolded as the junior officers arrived at the property.
The quartet of officers had been sent to the remote location following a request from NSW police trying to locate Nathaniel Train, missing from his western NSW home for almost a year.
"That request was given to the local police to go to this address to check on that missing person," Carroll said.
People had been in touch with the missing man before contact was lost in recent days.
Constables Arnold and McCrow were stationed at nearby Tara.
Queensland Police Commissioner Katarina Carroll. – AAP
Commissioner Carroll said the horrific incident was devastating for the victims' families and the entire force.
"Losing one of our own has a profound impact on every single officer and their families,'' she said.
"To lose two officers in one incident is absolutely devastating."
The commissioner fought back tears as she confirmed the initial deaths of her two officers and the neighbour, at a late-night media conference.
"I would like to also pay tribute to all police and first responders who assisted at the scene and are continuing to respond this evening," she said.
"Tragically, this is the largest loss of life we have suffered in one single incident in recent times. It is devastating news."
An emergency declaration remains in place for the Wieambilla area and a crime scene had been established at the property.
Leavers said "the behaviour of these murderers is absolutely unacceptable". He said the dead officers had “no chance” when fired upon.
“To know that she and he are no longer with us in what was a ruthless, calculated and targeted execution of our colleagues and loved ones brings home the very real risks that we face every single day doing our jobs,” Leavers said.
“They were executed by remorseless, ruthless killers.”
Prime Minister Anthony Albanese paid tribute to the slain constables, Mr Dare and the entire "close-knit and caring" Queensland community, saying it was a tough day for all Australians.
"This is, indeed, a devastating day for everyone who loved these Australians," he said.
"This is not a price that anyone who puts on the uniform should ever pay. We can never count the true cost."
"My heart goes out to the families and loved ones of all those affected by this tragedy. With honour they served, and Australia mourns with you today."
Opposition leader Peter Dutton, a former Queensland police officer, was also moved by the tragedy.
"Deeply distressing news coming out of western Queensland tonight with those police officers who have been murdered," he wrote.
"Police officers face danger every day to keep us from it."
"When you have a few police officers who are turning up to check an address, walking up the driveway and they're gunned down in a cold-blooded style, that will send a shiver down the spine of any police officer attending any job today," he said.
"Of course the police family is absolutely devastated, people will be scarred from the experience ... it's time for our community, for our country to come together around police and support them."
Queensland Premier Annastacia Palaszczuk said the deaths were a "horrible tragedy".
Palaszczuk said flags would fly at half-staff on government buildings across the state, while Brisbane's Story and Victoria bridges will be lit blue and white in mourning.
"Hopefully it will give the QPS family some comfort that the people of this state absolutely respect and appreciate every single thing that they do," she said.
"I doubt that this will bring much comfort to the families and loved ones of those who were killed.
"They were so young, so young, they were incredibly bright, these were absolutely callous, brutal acts."
Western Downs regional council mayor Paul McVeigh said his community was shattered.
"It's an absolute tragedy in our community," McVeigh said.
Nationals leader David Littleproud, who grew up in the area where the incident occurred, said the community was numb in the wake of the shooting.
"Chinchilla and Tara are both quiet, peaceful country towns. The shocking event that unfolded yesterday is not what our community is," he said.
"My thoughts are with the two brave police officers and the member of the public who lost their lives. The police community will be raw today and we grieve with them."
Greens leader Adam Bandt said news of the shooting was horrific.
"It's just a reminder of the risk and the danger that so many first responders put themselves into. You don't want to be reminded of it in that way," he said.