Emergency services were called to deal with a fire aboard a Stena Line ferry heading for Belfast on Monday evening.
Coastguard and lifeboat crews were sent to the ferry sailing from Cairnryan to Belfast at 9pm on Monday.
Fire broke out in the engine room of the Superfast VIII.
The ship was due into Belfast at 9.45pm.
It is now being brought in with the assistance of tugs - the fire is extinguished.
Coastguard teams from Bangor, Portaferry, Larne and Portmuck attended.
Passengers were told to congregate in designated areas after an emergency was declared.
Speaking to the BBC passenger Chris Clotworthy said code words were announced over the ship intercom.
He said: "The boat did a complete 180 degree turn and looked to be heading back to Scotland, this was when it was level with Blackhead (in County Antrim). It then did another complete 180 and stopped."
Mr Clotworthy said people were "relatively calm".
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