A second crewman is understood to have died following an accident this afternoon aboard a Panamanian-registered tanker 130 miles off the coast of Co Mayo.
ireland.comunderstands the accident happened when crewmen were attempting to secure a lifeboat during difficult weather conditions.
It is thought a number of crewmen were thrown on to the deck. One of the Argentinian crew died and two were seriously injured. One of the injured men has since died. No other vessels were involved in the incident and the Department of the Marine said the vessel, a 60,000-tonne tanker, is undamaged.
The rescue attempt is being co-ordinated by the Clyde Coast Guard and the Shannon-based rescue helicopter is on its way to the scene.
It is not yet clear what action will be taken as the weather conditions are severe with Force 11 winds and 8-9 metre swells.
The accident happened on board a Panamanian registered gas-oil tanker, the Princess Eva,which is en route from Copenhagen to Corpus Christi in Texas.