The Sea-Watch 3, run by NGO Sea-Watch, has been stranded on the Mediterranean for over a week with more than 30 migrants on board.
Another ship from the NGO Sea-Eye picked up a further 17 people who had been stranded on a fishing boat on Saturday.
Both ships are searching for a safe port. Sea-Watch posted on Twitter that it was time for “the German government to take responsibility.”
A spokesman for the group, Ruben Neugebauer, said that the Sea-Watch 3 was flying under a Dutch flag and was currently just south of Malta. He also said that the situation on board was stable, but that changing weather conditions next week meant the ship needed to find a port soon.
“We absolutely need a solution in this year,” he said.
There is disagreement in the European Union over who should assume responsibility for migrants rescued at sea, and Malta and Italy have closed their ports to NGO rescue vessels.
Hostility towards the NGOs has led to repeated cases of migrants languishing at sea for days on end with nowhere to go. The Sea-Watch 3 was impounded by Malta for a spell earlier this year as part of the clampdown.