French President Francois Hollande has called on European interior and foreign ministers to gather for an urgent meeting after a boat with up to 700 migrants capsized in the Mediterranean.

In an interview with France's Canal+, Hollande said urgent measures are needed to tackle "this kind of [people] trafficking, because those who bring people onto such ships are traffickers, even terrorists," Hollande warned.

He said the number of vessels and aerial vehicles patrolling Mediterranean waters and the air above, respectively, should be swiftly increased.

Twenty ships and three helicopters are taking part in a rescue operation off the coast of Libya south of the Italian island of Lampedusa.

Earlier reports by the Times of Malta suggest the migrants piled up on one side of the ship (which they were using to make it to Italy) in order to attract the attention of a Portugal-flagged ship.

Just for the record today's #migrant tragedy will be the worst tragedy at sea since WWII. #NoMoreDeathInTheMed

— Mark Micallef (@mmic78) April 19, 2015

Italy is to hold its own emergency cabinet meeting at 16:00 CET.