Italian and Maltese rescuers have saved more than 1,000 migrants in rough seas off Sicily since Thursday, authorities revealed.

The update on Friday came a day after navy helicopters spotted four migrant boats struggling to stay afloat in the Mediterranean Sea, as the immigration crisis that killed hundreds in shipwrecks in 2013 showed no signs of letting up in the new year.

The 823 men, women and children rescued from the four vessels were from countries including Egypt, Pakistan, Iraq and Tunisia.

In an earlier, separate operation, the navy rescued 233 migrants from Eritrea, Nigeria, Somalia, Zambia, Mali and Pakistan and took them to a port on Sicily's eastern coast.

The first boat was first sighted by a navy helicopter on Wednesday night as it ran into difficulty off the southern island of Lampedusa. The fiberglass vessel was packed to overflowing as it tried to cross the Mediterranean waters near Lampedusa, south of Sicily.

Italy sea arrivals triple

Each year, thousands of migrants and refugees attempt risky voyages across the Mediterranean in unseaworthy boats, and hundreds die en route.

Sea arrivals to Italy from Northern Africa more than tripled in 2013, fuelled by refugees from Syria's civil war and

political strife in the Horn of Africa.

Figures from the Italian Interior Ministry show about 25,000 migrants arrived by boat in 2013, with 10,000 of them fleeing conflict in Syria.

In October, 366 Eritreans drowned in a shipwreck near the shore of the Italian island of Lampedusa.