An alarm was sparked after a fire broke out on a Stranraer to Belfast ferry carrying about 600 passengers and crew.
The incident happened on the 1000 BST sailing of the HSS Voyager.
Stena Line's Irish Sea route director Alan Gordon said the fire, in a sealed turbine unit in the engine room, was put out by an automatic system.
Life jackets were given to everyone on board in accordance with safety procedures and the ferry continued its journey. Nobody was injured.
A total of 555 passengers and 46 crew were on board when the fire broke out at about 1040 BST.
The incident was brought under control within less than an hour.
A spokesman for the Maritime and Coastguard Agency said it would be checking the ferry when it arrived in Northern Ireland.
Tony Skeats, of the Belfast Marine Office, said: "We will visit the Stena Voyager when it docks at Belfast to ascertain the safety and integrity of the vessel before we allow it to continue to operate.
"It will be subject to a mechanical investigation to determine the cause of the fire."