A riot involving hundreds of asylum seekers at the Nauru immigration detention centre has been described as "the biggest, baddest ever" by a witness.

Up to 60 detainees were held overnight at the island's police station following the outbreak of violence on Friday afternoon.

There were reports up to 500 people may have escaped the facility but a spokeswoman from the Australian Immigration Department said the situation was under control on Saturday morning.

"All staff and transferees have been accounted for," she said.

The spokeswoman was unable to confirm reports a policeman had been stabbed before being held hostage.