Federal police say they cannot be sure all detainees are back inside the Christmas Island detention centre after recent escapes.
The centre was the scene of destructive riots last week. Up to 170 detainees roamed the island unchecked after a perimeter fence was pushed down in mass breakouts.
Australian Federal Police (AFP) officers were rushed to the island to quell the riots and have taken control of the centre from the contracted private operator Serco.
At a community meeting on the island on Tuesday morning, AFP Detective Superintendent Chris Lines said there were discrepancies in a head count conducted by Serco over the past 24 hours.
He said a more detailed head count was under way, matching detainees to photographic identification.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
"This will take some time, and it's not helpful to speculate on specific numbers of detainees that may be unaccounted for at this time."
Det Supt Lines said the discrepancy related to "a very small number" of detainees.
The breakouts and riots, in which accommodation tents and small buildings were burnt down as police battled rock-throwing rioters with tear gas and "bean-bag bullets", have heightened the island community's safety concerns.
Det Supt Lines said police, who now number around 190 on the island, were conducting regular patrols through the community.
A night-time curfew has been imposed at the Northwest Point facility where police in riot gear on Monday entered compounds and separated and moved certain detainees.
The perimeter fence at the centre has been electrified since Friday night.
Det Supt Lines said police had searched a coastal area on Monday after a reported sighting of an escapee, but found nothing.
