Surviving migrants float aboard a life raft near where their boat capsized.

Hundreds of migrants trying to reach across the Mediterranean from Libya are feared to have drowned after their fishing boat capsized off the North African country.

Statements on Twitter by UNHCR officials suggest that 399 people have been rescued so far and another 25 confirmed dead out of an estimated 600 migrants on the boat.

Karl Stagno-Navarra, a journalist based in Valletta, Malta, told Al Jazeera that an Irish navy vessel confirmed that the boat capsized when the people on board rushed to one side when the LE Niamh got close to it.

“The Irish vessel LE Niamh was present in the area, as part of the EU-sponsored operations dealing with migration at sea,” he said, adding that it approached the migrant boat after picking up a distress signal.

The Italian coastguard, a vessel of the Malta-based Migrant Offshore Aid Station and representatives of Doctors Without Borders (MSF) are also present at the scene participating in the operation, Stagno-Navarra said.

“There have tragically been many deaths, but [the MSF] does not have figures at this stage,” MSF said on Twitter.

Stagno-Navarra said: “This is an extremely difficult operation as many migrants do not know how to swim and the conditions are reported to be windy and stormy.” (Al Jazeera)