Probe over riot at Australian asylum centre Published duration 22 April 2011

media caption Nick Bryant on the riot at the Villawood Detention Centre in which nine buildings were set alight

Australian police are questioning 22 people after a riot at an immigration detention centre in Sydney.

About 100 people were involved in the riot, during which nine buildings at Villawood detention centre were torched.

Officials said that the situation was now calm but a number of detainees remained on the roof.

The government said the rioting was started by asylum-seekers who had had their visa applications rejected.

Immigration officials said that 22 people had been moved from the facility to a prison as part of a criminal probe into the riot, which began on Wednesday night.

"This sort of behaviour is absolutely unacceptable," Deputy Prime Minister Wayne Swan said. "They will certainly feel the full force of the law."

Villawood detention centre holds both irregular maritime arrivals - people arriving in Australia by boat to seek asylum - and people already on the Australian mainland who have violated their visas or had them cancelled.

The riot there was the latest in a series of protests and suicides at Australian immigration detention facilities.

In recent months the number of irregular maritime arrivals has increased, leading to overcrowding.

Critics say the detainees - mainly from Sri Lanka, Afghanistan and Iraq - are held in poor conditions and are unhappy with the length of time taken to process their applications.

In February riot police were drafted in when detainees at Australia's offshore detention centre on Christmas Island rioted.