Three protesters remain on the roof of the Villawood detention centre in Sydney's west amid Opposition calls for immediate police intervention.

One protester voluntarily came down from the roof about midday and has been receiving medical treatment.

The Federal Opposition says police should immediately force the remaining protesters down from the roof to regain control of the western Sydney facility.

The rooftop protest follows riots earlier in the week, which saw nine buildings destroyed by fire.

Twenty-two detainees have been taken to Sydney's Silverwater jail for questioning but no charges have yet been laid.

Federal Opposition Immigration spokesman Scott Morrison says there should be police intervention and the Government must take a stronger stance.

"What is needed is for the police to take control of the situation and for those men to be brought down and that the normal processes of justice are applied," he said.

"There should be no special rules for people breaking the law in detention centres, as opposed to those outside detention centres.

"There should be one rule for all and those involved in criminal acts should be prosecuted and charged. If you want to get in the line for a visa, then you can't get in the line for violence and if you do that, then you can't get a visa."

The Immigration Department has also confirmed that two people have escaped from residential houses attached to Villawood.

A spokeswoman says two others who tried to escape were arrested soon afterwards.

She says the houses hold low-risk detainees separately from the general detention centre.

The Australian Federal Police says its emphasis is on the security and safety of the protesters and that no further comment is appropriate.

The Immigration Department says Villawood Detention Centre is calm, despite the ongoing rooftop protest, and denies the centre is in lockdown.

A spokeswoman says the department is working hard to restore key services to detainees.

Ian Rintoul, from the Refugee Action Coalition, says he is concerned that the 22 men being held in prison over the riot are not being made aware of their rights.

"In many of the countries they come from [people are] seized by the police and placed in jail in places where they have no legal rights," he said.

"They do not necessarily understand that they don't have to give a statement. They don't have to talk to the police.

"We are very concerned that no statements are made and there are no interviews with the police until they understand their rights."

The men are believed to be protesting against their failed visa applications.

The protest reached its peak when a small protest on Wednesday afternoon developed into a full-scale riot in which close to 100 asylum seekers burned down nine buildings at the centre.

A computer room, kitchen and medical centre were destroyed by fire and a large gas cylinder also exploded.

A former Villawood guard told ABC Television's Lateline program on Thursday that problems at the Sydney centre have been building for some time and he is not surprised about the riots.

In a statement, Serco, the private operator of detention centres in Australia, acknowledged an increased number of arrivals and longer periods of detention have placed significant pressures on their operations.

The company said it has provided additional training to staff beyond contractual requirements and has invested $1.5 million in staff training.

Villawood is the second Australian immigration detention centre to be set on fire this year.

A Federal Government-ordered review into riots at the Christmas Island centre in March, which saw tear gas and bean bag rounds being fired at asylum seekers, will now also investigate the Villawood protests.

Meanwhile, the Immigration Department has confirmed three former detainees convicted over the 2009 Christmas Island riots have since been granted visas to stay in Australia.

Mr Morrison says it makes a mockery of the immigration system and of the Government's claims it will use its powers under the migration act to weed out people of bad character.

"I think what it does at the end of the day is proves hollow, the resolve and threats of the minister to take action when clearly he has been put to the test and has failed," he said.