The police worker was shot at close range on Friday afternoon in the street outside Parramatta’s police station in western Sydney.
“It appears an officer has discharged his weapon, responding to a report that a person had been shot”, NSW Police said in a statement.
“We’re a long way from establishing a full picture of this man, and his exact motivations still remain a mystery to us”, New South Wales police commissioner Andrew Scipione said.
Eyewitness reports suggest the teenager, who is yet to be named by authorities, shouted religious slogans before firing one shot in the back of the head of a police finance worker, a father of two, as he left work.
The civilian was an information technology specialist for the police.
Scipione said police were already on high alert for football finals being held this weekend in both Sydney and Melbourne, but all officers and security officials are being informed to take extra care. Prime Minister Malcolm Turnbull, who described the terror-related shooting as a “cold-blooded murder”, echoed the commissioner’s comments.
Police helicopters are overhead at the scene. “We can not let hate overtake us”, Baird said.
Aerial images from Channel Seven news showed what appeared to be two bodies covered in white sheets outside the headquarters of New South Wales police.
He added: “And then within half a minute of that there were three or four more bangs”.
Referring to terrorism as among the challenges Australia faces, he stressed that “they must never divert us from our commitment to being free Australians, working together to ensure we achieve our common goals”.
“I can tell you that this was a brutal crime, a bad crime”.
Two people are believed to have been shot dead in Parramatta.
Mr Baird said it was a “chilling act” and his thoughts were with the family of Mr Cheng.
“I heard what sounded like a couple of gunshots, but assumed it was tradies… they’d dropped a plank or something”, he told 9NEWS.