A police IT worker has been "callously murdered" and his killer shot dead as officers returned fire outside the force's headquarters in Sydney's west, NSW Police Commissioner Andrew Scipione has confirmed.
The identity of the lone gunman and his motive have not been established, Mr Scipione said at the scene of the shootings in Parramatta on Friday evening.
He said the civilian police employee was shot at close range with a handgun as he left the building for the day.
"I can tell you that this was a brutal crime, a terrible crime," he said.
Mr Scipione said the IT specialist was "simply leaving work" at the State Crime Command on Charles Street about 4.30pm when he was deliberately targeted and killed.
Three other officers then came under fire.
Witnesses reported seeing a man in a black gown pacing, yelling and wielding a gun outside the police centre moments before a series of shots were heard.
Real estate agent Edwin Almeida said he later saw two bodies on the pavement.
He said one belonged to the man in the black gown and lay in a pool of blood.
Mr Scipione said there was nothing to suggest the shooting was terror-related but he refused to rule anything out as investigations continued.
He said it was likely the gunman waited around after the murder in order to "commit suicide by cop".
The phrase refers to someone who deliberately provokes a lethal response rather than allowing themself to be arrested.
"He remained in the street and was acting quite aggressively ... it's likely he was firing shots," Mr Scipione said.
A broad exclusion zone was set up around the crime scene with several buildings still in lockdown more than four hours after the shooting.
Residents returning home from work were left stranded in the streets, waiting to access homes.
Several children were also stuck inside a nearby daycare centre with worried parents forced to congregate outside.
But Mr Scipione confirmed the children were safe and had since been released.
He said police may boost security in Sydney for the NRL grand final on Sunday in the wake of the incident.
"Obviously this is a very distressing time for us all," he said.
"We've just been through Police Remembrance Day only Tuesday this week and here we are on Friday having to deal with this.
"(But) we will go and get to the bottom of this."
Mr Almeida said his frightened staff ran into their office as the drama erupted before hearing three to four gun shots.
"We looked out the window, saw security guards and what appeared to be a plain clothes police officer with gun drawn and pointing at the person that was now lying on the floor surrounded by a pool of blood," he told AAP.
"We asked our staff to come inside because it appeared to be a serious situation."
Police confirmed a major operation was underway between Hassall Street and Charles Street with the public told to avoid the space shortly before 5pm.
