As many as 700 people may have died in the capsizing of a boat carrying migrants across the Mediterranean, media reports indicated Sunday. The incident took place just outside of Libyan territorial waters late Saturday near to the Italian island of Lampedusa.

An emergency was declared around midnight local time, after the boat's passengers are believed to have capsized their vessel, by moving to one side in a bid to signal a passing merchant ship, the Times of Malta reported.

European Union leaders considered calling a special meeting to deal with the immigrant issue, Reuters reported.

"At the moment, we fear that this is a tragedy of really vast proportions," Carlotta Sami, a spokeswoman for the United Nations High Commissioner for Refugees, told SkyTG24 television, Reuters reported.

Thus far, a rescue operation involving the Maltese navy, Italian ships and commercial vessels has managed to rescue 28 people. Maltese Prime Minister Joseph Muscat tweeted that many of the boat's passengers were feared to have been killed. He estimated the number of people on board the vessel at 650.

A spokesperson for the Italian coastguard told the BBC: "At the moment, this is still a search and rescue operation, but in time it will be a search [for bodies] only." He added that 20 ships and three helicopters were currently involved in the rescue.

The incident echoes another recent tragedy in the region, which saw up to 400 migrants drown after their boat capsized off the coast of Libya. In that incident, 144 people were rescued, according to the Guardian.

Southern Europe has been contending with a humanitarian crisis in recent years, as increasingly desperate migrants from the Middle East and Africa set out on the treacherous journey across the Mediterranean in ramshackle boats, in a bid to reach Europe. Huge numbers have died on the crossing, and European authorities have been unable to find a solution to the crisis.

This is a developing story. Check back for further updates.