Rescuers are searching for hundreds of migrants in the Mediterranean after a boat carrying as many as 600 people capsized off the coast of Libya.

The Irish navy said "significant loss of life" was feared and Medecins Sans Frontieres confirmed "many deaths".

"We don't know how many people might be trapped within the belly of the boat that capsized and sunk, that's our greatest fear," said Will Turner, emergency coordinator at Medecins Sans Frontieres.