A fishing boat carrying an estimated 600 migrants has capsized north of Libya’s coast, Irish navy officials said.
Captain Donal Gallagher said that some 150 migrants were spotted in the water yesterday morning and that rescue efforts by several ships were under way.
An Italian military helicopter was lowering life rafts.
The Irish naval vessel Le Niamh was one of several ships requested by the Italian coastguard to speed to the rescue Capt Gallagher said.
Also involved in the rescue were an Italian vessel and a boat operated by Doctors Without Borders.
Non-governmental organisations often join in migrant sea rescue operations, which are co-ordinated by Italy’s coastguard and are now under the umbrella of a European Union task force known as Triton.
The distressed vessel was reported to be about 75 miles north west of Tripoli, Libya’s capital.
Officials have yet to determine what caused the capsizing.
The International Organisation for Migration, a human rights group, has said nearly 2,000 migrants are believed to have died at sea since the start of this year, but the exact toll of dead is not known.
In April, a smuggling boat crammed with about 800 migrants overturned, also off Libya’s coast where smugglers operate. Only 28 survivors, including two alleged smugglers, were found.
Fleeing war, persecution and poverty, the migrants travel overland for weeks or months from sub-Saharan Africa, the Horn of Africa, the Middle East and parts of Asia to reach Libya. There they set sail in flimsy motorised rubber dinghies or rickety old fishing boats.
When the boats have problems, someone aboard contacts the coastguard by satellite phone requesting rescue. Other boats in distress are spotted by Triton air surveillance.
Most of the migrants hope to find asylum, relatives or jobs, mainly in northern Europe.