At least four people dead and 51 missing as migrant ship sinks off Tunisia

Shipwreck comes as two boats sink off of Italian coast

More than 20 migrants drowned after a boat capsized off Tunisia in May last year. AP

At least four people died and 51 were missing after a migrant ship sank off Tunisia's Kerkennah island.

All aboard were migrants from sub-Saharan Africa, an unidentified judicial official told Reuters on Sunday.

It came the same day as rescuers looked for 30 missing off the coast of Italy after two boats sunk in rough seas on Saturday.

Both were rickety iron boats believed to have departed from the Tunisian city of Sfax on Thursday.

Tunisia is now the main departure point for people fleeing poverty and conflict in Africa and the Middle East in hopes of a better life in Europe.

Many boats, often flimsy vessels unable to withstand the treacherous crossings, do not make it to their intended destinations in Italy.

The Tunisian coastguard recovered a record 901 bodies of drowned migrants off its coast from January 1 to July 20, the country's interior minister said.

The country has responded to the migrant influx by deporting hundreds to remote desert areas where it hopes they will cross the border into Algeria and Libya, previously the main hub for departures to Europe.

The UN has urged Tunis to halt migrant expulsions to the border buffer zone, where at least 11 people have already died in scorching summer temperatures with no food or water.

It began forcing migrants to the border after clashes between locals and migrants left one person dead in Sfax last month.

Tunis responded by denying the severity of the crisis, saying the issue was being manipulated for "political motives".

Migrants braving the sea crossing also face huge dangers – described as a "slaughter" by sea by an Italian official on Sunday.

"Whoever allowed them, or forced them, to leave with this sea is an unscrupulous criminal lunatic," police chief Emanuele Ricifari of Agrigento, Sicily told Italian media after the twin shipwrecks.

The Central Mediterranean migrant crossing route from North Africa to Europe is the world's deadliest.

More than 1,800 people have died attempting it so far this year, according to the Italian Coastguard – almost 900 more than last year.

"The truth is that figure is likely to be much higher. Lots of bodies are being found at sea, suggesting there are many shipwrecks we never hear about," coastguard press officer Flavio Di Giacomo told AFP.