A rescue operation is continuing on Carlingford Lough after a fisherman was rescued off Greencastle.
Another man is still missing and coastguard units from both sides of the border are involved in the search.
The Department of Transport said the Coast Guard received a report the vessel was in trouble near Greencastle Point, Co Down, shortly after 12.30pm.
One person was recovered from the vessel by a local boat and transferred to the care of HSE paramedics at Greenore harbour.
A search was ongoing to recover a second person.
It is understood the two men are from a local fishing boat and were working the waters off Greencastle when their boat sunk.
An RNLI lifeboat from Kilkeel and the Greenore Irish Coast Guard boat were sent, along with Coast Guard rescue teams from Newcastle and Kilkeel.
The Irish Coast Guard's Rescue 116 helicopter took part in the search and a Royal Navy helicopter assisted.
Gardaí said they were also on the scene.
The Marine Rescue Co-ordination Centre (MRCC) in Belfast was coordinating the response.
Additional reporting by PA
