The young men, mostly Sudanese, who had left Libya late on Saturday in a blue rubber dinghy, clapped and cheered as the ship came into view.
Sunday's rescue was the third in as many days.
The ship, jointly operated by SOS Mediterranean and Medecins sans Frontieres (MSF - Doctors Without Borders), has been patrolling international waters some 50 nautical miles off the coast of Tripoli.
"We're the only ones in the area, the Libyan coastguard don't respond" to distressed migrant vessels, SOS Mediterranean search and rescue coordinator Nicholas Romaniuk told AFP.
Romaniuk said fair weather conditions would likely encourage more departures from Libyan shores.
A further incentive is that a three-day Muslim holiday, Eid al-Adha, which kicked off on Sunday, may reduce the presence of authorities patrolling Libyan beaches.
About two-thirds of those aboard the Ocean Viking are Sudanese.
The group rescued on Friday were from West Africa, mainly from Senegal as well as Ivory Coast, who had come to Libya to work but got caught up in the fighting in the lawless North African country.
MSF, which registers the migrants on board, said Sunday that four-fifths of the latest group to be rescued were aged between 18 and 34, while 17 percent were under 18.
The rescues come at a time of tension between Italy and other EU states, with the Italian government refusing to let migrants land on its shores unless its EU partners help take them in.
The Ocean Viking is registered in Norway, and Italy's far-right Interior Minister Matteo Salvini sent a warning to Oslo last week.
"Italy is not legally bound, nor disposed to take in clandestine, unidentified migrants from on board the Ocean Viking," Salvini wrote.
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![Libya coastguard [Getty]](/sites/default/files/media/images/4AC5D4D8-C1ED-40F8-803E-8C7D00C87327.jpg "Libya coastguard [Getty]")
