The man on the roof of an immigration centre in Lincolnshire is a Chinese national. Staff at Morton Hall near Lincoln said he took to the top of the 30 foot high building at 1130 BST.
Trained staff are on the roof trying to negotiate with the man who is not said to be making demands. Emergency services were on scene, although several fire engines have now left.
Lincolnshire police were called to a similar incident yesterday when a different detainee also got onto the roof but that was quickly resolved.
More top news
Operation Shimmer is targeting the minority of cyclists in the city who cause a danger to themselves and others by cycling without lights.
Weather: Weekend update with Emma Jesson
Detectives have released a CCTV image of a suspect they would like to identify after a man was stabbed in an attempted street robbery.