The Ocean Viking, a rescue ship chartered by SOS Mediterranee, rescued 68 stranded migrants in international waters off Libya on Sunday, the France-based humanitarian NGO announced.

"The Ocean Viking rescued 68 shipwrecked people from a double-decker wooden boat that left Zouara in Libya last night," the NGO said.

"Several of them are suffering from seasickness and are currently being treated by the medical team of SOS Mediterranee and the International Federation of Red Cross and Red Crescent Societies (IFRC) on board the Ocean Viking," it added.

Images published by the NGO on X, formerly Twitter, show several dozen migrants crammed into a makeshift boat wearing orange life jackets.

The Italian authorities have ordered the NGO to disembark the survivors at Ancona, a distant port to which the organisation has objected.

"The port is 1,560 kilometres (970 miles) -- four days' sailing -- from the area of operations, at a time when there is a crucial need for search and rescue capacity in the Mediterranean. There are many boats leaving shore and the risk of loss of life is high", it said.

Since coming to power in 2022, Giorgia Meloni's far-right government, which includes anti-migrant League leader Matteo Salvini as deputy prime minister, has stepped up measures to hamper the activities of migrant rescue charities.

At the end of August, the Ocean Viking rescued 440 migrants in distress in international waters off Libya and Tunisia before heading for Genoa, northern Italy, the remote safe port assigned to it by the Italian authorities to disembark the survivors.

The central Mediterranean is the most dangerous migratory route in the world, according to the International Organization for Migration (IOM).

The United Nations agency estimates that since the beginning of 2023, 2,013 migrants have gone missing in those waters, compared with 1,417 for the whole of 2022.

In June, at least 82 people died in a shipwreck billed as one of the most serious involving migrants in the Mediterranean.

The Ocean Viking was detained for 10 days in July by the Italian authorities, who alleged there were safety issues with the vessel, but it was authorised to set sail again on July 21.