NSW Police will conduct round-the-clock patrols of Sydney's iconic landmarks and major transport hubs amid a heightened security threat after yesterday's counter-terrorism raids across the city.

Operation Hammerhead will see hundreds of officers maintain a highly visible presence 24/7 at locations, including the Sydney Harbour Bridge, the Opera House and surrounding foreshore, and at sporting events and large public gatherings.

The security boost comes after synchronised dawn raids Thursday on houses and vehicles across Sydney's west and north-west, and in Brisbane's south, involving more than 800 police.

The raids foiled a plot involving a man believed to be Australia's most senior Islamic State member who called contacts in Australia and asked them to carry out a campaign of random public beheadings in Sydney and Brisbane, the ABC understands.

Mohammad Ali Baryalei, a Former Kings Cross bouncer and part-time actor, was understood to have issued the instruction to kidnap people in Brisbane and Sydney and have them executed on camera.

The video would then be sent back to IS's media unit, where it would be publicly released.

Omarjan Azari, 22, from the western Sydney suburb of Guildford, was one of 15 people detained during the operation in Sydney and is accused of conspiring with Baryalei and others to act in preparation or plan a terrorist act or acts, court documents show.

Commonwealth prosecutor Michael Allnutt told Sydney's Central Local Court the alleged offence was "clearly designed to shock, horrify and terrify the community".

Mr Allnutt said there was "a plan to commit extremely serious offences" that involved an "unusual level of fanaticism".

Close ties with Sydney Islamic community a priority: police chief

NSW police say contact within Sydney's south-west Muslim community will also be a high priority in the wake of the raids, with Police Deputy Commissioner Nick Kaldas saying the majority were law-abiding citizens.

"I think the Muslim community are - by and large the vast majority of them are - horrified that anyone in Australia would think things like that," he said.

"They would really rather this sort of thing didn't happen," he said, adding they would prefer the Islamic community not be seen as having produced those accused of terrorism offences.

"I think the vast majority of the community are doing their best to make sure that this sort of radicalisation doesn't occur and doesn't get people to a point where they become accused of these sorts of things."

Deputy Commissioner Kaldas, who has been involved in every main anti-terrorism investigation in Australia in the past decade, said technology was playing a major role in spreading messages of terror.

"One of the things that has changed is the immediacy and the high impact of very graphic material being broadcast on Twitter and Facebook, and all sorts of social media," he said.

"It is definitely having an impact on people on the ground here, not just in Sydney but across the world.

"Some people may find some sort of perverse inspiration in it, but the availability of large amounts of material in this way is definitely something different that we have had 10, 20 years ago."

Operation Hammerhead is expected to last for a few weeks.

"This is something we'll do for a week or two but beyond it is a long term thing, certainly the engagement part of it is a long term thing," Deputy Commissioner Kaldas said.

"It is simply core business for us, although we are escalating and enhancing it in the coming days and weeks."

New Catholic Archbishop calls for humanitarian approach

The newly appointed Catholic Archbishop of Sydney, the Reverend Anthony Fisher, has called on the community to show "humanitarian concern and respect" after the raids.

Police have been accused of using unnecessary force during the raids, and one man, Maywand Osman, said he was beaten at his home in suburban Marsfield by police before being released without charge.

Maywand Osman says he was assaulted while being detained during the raids. ( Supplied )

About 200 people from Sydney's Muslim community held a protest against the raids outside Lakemba station on Thursday night.

The group heard claims of police brutality and political hysteria, and the speakers included children who said they witnessed one of the raids.

One said he and his mother were assaulted.

"I think at times like this we need the wisdom of the great spiritual traditions about restraint, about peacemaking, about humanitarian concern for each other, about respect for each others religious beliefs and for religious liberty," Bishop Fisher said.

"Australia should continue to give the world the example of people of every nationality and religion and background being able to live as neighbours."