Immigration Minister Chris Bowen has indicated he may cancel the visas of any "non-citizens" charged after the weekend's violent protests in Sydney.

Six people have so far been arrested after police on Saturday clashed with Muslim protesters who were angry about an online video that mocks the Prophet Mohammed.

The violence has been condemned by political leaders and many Muslims, but one Coalition senator says it should serve as a "wake-up call" to those who are "naive" about the potential impact of Islamists in Australia.

"It is easy to dismiss the practices of the last week as the result of some crazy extremists," Senator Cory Bernardi wrote on his website.

"That is the convenient route for those who know very little about the fundamentalist Islamic agenda and understand little of their mission worldwide."

Fellow Coalition MP George Christensen says those found guilty of violence should be deported if they are not Australian citizens.

"I think the average Australian would think (that) if you're engaging in violence and you weren't an Australian citizen, jump on the first plane and head back to where you come from because that stuff is just simply not on in this nation," Mr Christensen told ABC News Online.

"It really does call into question the whole thing that's been pushed for the last 20 to 30 years on multiculturalism.

"When we see scenes like that, we just wonder what the future may hold."

Mr Bowen says he is looking at what options he would have if any "non-citizens" were involved in the protest, but has spoken out strongly against the violence.

"Clearly this is not done in the name of Islam and it is not done in the name of multiculturalism; it's done in the name of thuggery, nothing short of that," he told reporters in Canberra.

"This is just criminal behaviour, nothing short of that."

Public anger

The wording of some placards have generated public anger. ( AAP: Louis Allen )

Much of the public anger over the weekend's events has focused on some of the placards held by protesters, especially one that read: "Behead all those who insult the Prophet."

Some of the placards were being held by young children, and they appeared to be encouraged to do so by their parents.

Mr Christensen has described those involved in writing and distributing the placards as "idiots".

"For those people who like to say that Islam is a religion of peace, well, if it's a religion of peace, I think Mohammed would be turning in his grave to see signs up saying let's behead all those who insult the prophet or insult Islam."

"Particularly when they're in the hands of youngsters and toddlers, it's just an absolutely disgusting situation."

Foreign Minister Bob Carr says the placards were the work of "provocateurs" trying to achieve an "extreme clash" between cultures, and has urged the community not to be provoked.

But he has conceded that he is a "little apprehensive" about the prospects of long-term peace between Muslim and Christian cultures.

"The way these demonstrations flared makes me a little apprehensive, but I do hope, and I think there's a chance of this, that they could recede every bit as fast and they came in," Senator Carr told ABC Radio National.

Prepared

Meanwhile, police have warned they will be prepared if there is a repeat of the protests in Sydney's CBD this weekend.

Commissioner Andrew Scipione has revealed that police were made aware about the protests when they were forwarded text messages from members of the Muslim community.

"Many of them were sent to us by people within the community who were outraged by what they were receiving on their SMS system or on their Facebook page, and so they brought them to our attention," he said.

"We have good relations with community and through the community contacts unit, which is an area where we invested very heavily in recent times."

Sorry, this video has expired Lots of work ahead for protest strike force

'Hate preacher'

The weekend protest took place in the lead up to a national conference being hosted by an Islamic group called Hizb ut-Tahrir (HUT) in western Sydney.

The conference, called Muslims Rise - Caliphate Imminent, encouraged the establishment of a global Islamic state and sharia law.

One of the keynote speakers was Taji Mustafa from the British arm of Hizb ut-Tahrir, whom the Opposition has described as a "hate preacher".

Opposition immigration spokesman Scott Morrison says Mr Mustafa should not have been given a visa to enter Australia.

"I am concerned about an organisation that has called for the military destruction of Israel," Mr Morrison said.

"I'm concerned about an organisation who believes in the restoration of the Caliphate.

"I'm concerned about an organisation that has condoned the killing of Australian troops in Afghanistan.

"I am concerned about an organisation that says democracy is forbidden."

Mr Morrison wrote to Mr Bowen in the lead up to the conference to seek the Government's reassurances that it would not allow Mr Mustafa to enter the country.

But in Question Time today Mr Bowen defended the Government's handling of the issue.

"HUT has not been proscribed (as a terrorist organisation) in Australia, nor has it been proscribed in the United States or the United Kingdom," he said.