Crew were evacuated from a North Sea oil rig last night after a fire broke out on board.

The Ocean Guardian, a semi-submersible rig owned by Diamond Offshore Drilling of Aberdeen, was operating 120 miles north-east of the city when the incident occurred.

As a major rescue operation swung into action, a second emergency call was received of a possible sighting of an aircraft coming down near Banchory. However, no trace of anything was found and no aircraft was reported missing, and the search was called off.

There were 87 crew on board the Ocean Guardian when the fire broke out in an engine room shortly after 6pm. As the rig's own fire teams began to tackle the blaze, a muster was called and 32 non-essential crew were evacuated.

Four helicopters were involved in the operation, the Bond Jigsaw 1 search-and- rescue helicopter on duty in that area with specially trained crew, two oil-support aircraft and the Norwegian Saver search-and-rescue helicopter.

Nineteen crew were taken to the nearby Andrew platform and a further 13 to the Brittanic platform.

The fire was reported to have been extinguished after an hour and the down- manning stopped.

A coastguard spokesman said: "The people remaining on the rig were able to fight the fire and it is now out. The company are now assessing the next step to deal with the situation."

A spokesman for Diamond Offshore said: "As a precaution we began down-manning non-essential personnel. Two helicopters lifted a total of 32 people off the rig.

"Fifty-five people are still on board and the incident is at an end. The fire is out and there are no injuries - everyone is accounted for."

The spokesman confirmed that an incident team would be sent to the rig to investigate the cause of the fire.

Graham Tran, of the Amicus offshore union, said: "It is important that the findings of the investigation are placed in the public arena.

"An investigation must be carried out to find out what happened and see if any lessons can be learned."

In the Banchory incident, at the same time, a member of the public called the police to report seeing flames coming from an aircraft followed by black smoke which quickly dispersed in the wind.

Police, the fire brigade and ambulance service, as well as a mountain rescue team, went to the scene at Hill o'Fare near Banchory, and a helicopter from RAF Boulmer near Alnwick in Northumberland was scrambled to search the area.

The A980 road was closed at Raemoir for some time because of the number of emergency service vehicles in the area, but nothing was found.

A police spokesman said: "It is believed to have been a well-intentioned false alarm."

It is understood a military operation was taking place in the same area as the reported sighting of the plane in trouble.