NSW Premier Mike Baird has warned that would-be terrorists will be hunted down and they were likely already being monitored.

NSW Premier Mike Baird has delivered a fierce warning to would-be terrorists: “We will hunt you down.”

“If you have any intent to bring overseas conflicts here, if you have any intent to threaten the security of this community, we will hunt you down,” the premier said following the pre-dawn counter-terrorism raids in Sydney and Brisbane.

“Those that think they may be operating in dark corners, we are shining the light upon you.

“You may well be listened to as we speak.”

Mr Baird said plans to randomly attack Sydneysiders were horrifying and those responsible would be caught.

More than 800 NSW and Australian Federal Police raided properties across the Sydney’s north-west and in Brisbane.

Fifteen people were detained and one has appeared before court.

Omarjan Azari, 22, from Guildford in Sydney’s west, has been charged with one count of acting in preparation/planning of a terrorist attack.

Azari is accused of being involved in a plan designed to “shock” and “horrify” through the “random selection of persons to rather gruesomely execute”.

Mr Baird said there would be a heavy police presence across Sydney’s iconic sites and transport hubs under Operation Hammerhead.

Their presence will be felt this weekend during the Sydney Running Festival and at NRL and AFL finals.

He urged people to go about their normal lives and not be scared off attending major events.

“It’s certainly not a time to panic,” he said.

“It is a time for calm. Be alert but be assured.”

NSW Deputy Police Commissioner Catherine Burn said authorities had been investigating the group for several months.

“Today has been about disrupting activity that we will be alleging in court related to some extreme violence being committed against a person,” she told reporters.

“We don’t know any specific details about that person or where that location potentially may have been.”

Ms Burn said police may lay more charges against the group in coming days.

Commissioner Andrew Scipione warned police would act against anyone who wanted to “turn against the Muslim communities”.

He praised as “first class” the level of police interaction with the Muslim community to “ensure that we get a safer Australia”.