'A Major Terrorist Attack In Australia Is Inevitable' Says Most Senior Police

A major terrorist attack in Australia is inevitable, according to one of the country's most senior police officers.

"I don't like to say it but it will happen. It's inevitable," NSW assistant commissioner for counter-terrorism Mark Murdoch has told News Corp Australia.

"Despite everything that is being done and the good work that law enforcement and intelligence is doing, without wanting to create unnecessary fear within the community, it's going to happen."

The 37-year police veteran, who will retire in November, said it was impossible to prevent extremist groups exploiting social media to lure young recruits who are almost completely unknown to authorities.

"We can manage what we know but not what we don't know and that's where the risk lies," he said.

A telling risk lay in dealing lone wolf groups such as those involved in the alleged July plot to blow up a Middle East-bound Etihad plane in Sydney, Mr Murdoch said.

The former homicide investigator caused waves at the 2015 inquest into the Lindt Cafe siege when he broke ranks by saying he thought police should have stormed the cafe after gunman Man Haron Monis fired his first shot instead of waiting another 10 minutes.

- AAP