Rescue ship Ocean Viking has saved more than 500 migrants adrift in the Mediterranean in operations over the last two days, the organisation that runs it, SOS Mediterranee, said.

The rescues took place southwest of Lampedusa, in the waters between the Italian island and Tunisia, the organisation said on Friday.

"Already 11 rescues have been carried out over more than 42 hours and more than 500 people have been rescued," SOS Mediterranee said.

They were helped on board the vessel by teams from the International Federation of Red Cross and Red Crescent Societies (IFRC), it added.

"Rescue operations are still going on in the search-and-rescue zone between Tunisia and Lampedusa."

The Ocean Viking was on Thursday alerted by the Italian emergency services and given the coordinates of vessels in distress southwest of the island, the NGO said.

The central Mediterranean Sea is the most perilous maritime crossing in the world for the migrants.

At least 1,848 people have died so far this year attempting the Central Mediterranean route from North Africa to Italy and Malta, according to the United Nations migration agency, the International Organisation for Migration.

That is significantly higher than its figure for the whole of 2022, which was 1,417.

In June, one sinking alone in the western Mediterranean cost the lives of at least 82 people, one of the deadliest incidents involving migrants in the area.

In July, the Italian authorities detained the Ocean Viking for 10 days at Civitavecchia port outside Rome, after questioning the vessel's safety standards before finally releasing it.