Police block the scene near New South Wales Police Headquarters in Sydney where a 15-year-old gunman shot dead a civilian police employee last Friday, before being gunned down by police.

AFP/Sydney

Australian Prime Minister Malcolm Turnbull said on Monday it was still not clear if the teenager who shot and killed a man outside a police headquarters was a self-motivated "lone-wolf" attacker.

Police have not identified the black-clad assailant who shot 58-year-old finance worker Curtis Cheng in the back of the head outside New South Wales state police headquarters in suburban Sydney on Friday.

The teen, who authorities said was born in Iran of Iraqi and Kurdish background and had no criminal history prior to the incident, was killed in an exchange of fire with police.

"In terms of these so-called lone wolves, it is too early to comment or really for me to say at any rate to what extent this individual who murdered Mr Cheng was self-motivated, self-activated," Turnbull told reporters.

"There is a lot of work being done to investigate this murder," said the leader, who on the weekend said the attack "appears to have been an act of terrorism".

Authorities have searched a mosque the shooter is believed to have attended, and Turnbull stressed that Australian Muslims were the country's "absolutely necessary partners in combating this type of extremist violence".

"All of us need to be very aware of the way in which radicalisation can occur... communities at every level, from families all of the way up, should be alert to what young people are doing, what influences are impacting on young people," he said.

Police have given no information on the shooter, who media reports said regularly skipped school to pray at a local mosque.

Australian officials have said they are concerned about the prospect of lone-wolf attacks by individuals inspired by groups such as the Islamic State organisation, and have cracked down on Australians attempting to travel to conflict zones such as Syria.

Turnbull said the government must adapt to changing threats and "constantly calibrate our response and learn from what we're doing".

"The need to counter radicalisation is there, the government's commitment to countering it is absolutely undiminished," he said.

Robyn Torok, an expert in online radicalisation from Edith Cowan University, told the national broadcaster ABC that Islamic State militants are recruiting young Westerners to launch attacks in their home countries.

"They're giving them information... on how to hide their extremist identity, how to fly under the radar, how to deal with certain agencies, how to buy certain weapons and how to hide their true intent," she said.