Britain evacuated oil workers from a North Sea accommodation platform on Sunday and sent in an explosive disposal team following reports of a bomb threat, officials said.
About 14 helicopters and a Nimrod reconnaissance aircraft were sent to the Safe Scandinavia platform in the Britannia oil field, 210 kms (130 miles) northeast of the Scottish city of Aberdeen, the officials said.
A spokeswoman for the Maritime and Coastguard Agency said about 500 oil workers were being evacuated to other platforms and there were no reports of any injuries.
Sky News said the evacuation operation followed a bomb threat. Officials said the incident involved a woman on board the platform but gave no details.
BBC News 24 quoted sources saying the incident was not terrorist-related.
The Ministry of Defence in London said it had responded to a request to provide a bomb disposal team.
"I think everybody is safe," a ministry spokesman said.
A Royal Air Force (RAF) spokesman said about 14 helicopters were involved in the operation.
"There's a security alert. We've been requested to send out helicopters," a spokesman at the RAF's Kinloss base said.