Fed police deployed on Christmas Island

Federal police remain in control of the immigration detention centre on Christmas Island.

Buildings and tents within the island's detention centre were set ablaze overnight, continuing four days of unrest in which federal police have been forced to use tear gas and non-lethal bullets.

The situation erupted during the early hours of Monday when several hundred detainees began rioting.

Immigration Minister Chris Bowen told reporters in Canberra there were 70 extra AFP officers on the way to the island bringing the total contingent to 188.

"AFP remain in control of the centre and will remain so as long as is necessary," Mr Bowen said.

Most detainees were not involved in the protests and were distancing themselves from the "unacceptable behaviour".

"A group of around 200 protesters seem to think violent behaviour is an acceptable way to influence the outcome of their visa application or influence government decision making," Mr Bowen said.

Mr Bowen said events of the past few days had made it necessary to reduce the number of detainees on Christmas Island.

At the start of this week there were 2500 detainees, down from the more than 3000 in December.

There were now fewer than that with the new detention centre in Darwin helping to ease pressure, Mr Bowen said.

"But clearly this reduction now needs to be expedited," he said, adding 105 detainees would leave the island on Friday and more on Saturday.

"They will be spread throughout our existing detention facilities (on the mainland)."

Mr Bowen delivered a blunt warning to those involved in the riots on Christmas Island.

"The migration act allows that character is an important consideration in determining whether somebody should be granted a visa," he said.

"This will considered on a case-by-case basis, but character considerations will be taken into account of those on Christmas Island that have organised and perpetrated this activity."

It was also necessary to "lift the bar" for those applying for a protection visa if they were regarded as a genuine refuge.

"I will be doing that very seriously on a case-by-case basis in relation to anybody who has participated in this sort of activity."

Assistant Commissioner Steve Lancaster said it was not known whether any detainees were still at large.

"We are still in the washup of identifying what went wrong and who was responsible," he said.

"Clearly there are people who potentially did get out and of course as we go through the processes of ensuring how many people are out - if any - we will deal with that issue."

Mr Bowen said that Christmas Island detainees were to get a visit from immigration department process officers this week but this would not now occur.

"We do not respond to these sorts of activities," he said.

"They will now go to other centres and will be processing other claims.

"So people in places where detention centres are operating as per normal will be able to progress that processing of refugee claims - that won't be possible at the moment at Christmas Island."

Mr Lancaster said the situation at the detention centre remained tense.

"My assessment ... is that with the strategy we have in place at the moment we should be able to deal with the incidents that could occur tonight," he said.

"However, at this stage it is deemed to be tense and I don't want to speculate on what might happen tonight.

"I believe we have the appropriate tools and people in place, with specialist capabilities and general duties, to deal with what we have before us."