Rescue ship Lifeline has not received official permission to dock in Malta, the German aid group told Euronews in an email on Wednesday.
“One day ago came the breaking news that we are allowed to enter Malta, but we still have no approval. We ask now if we are allowed to protect at least from the high waves and the strong wind off the Maltese coast. Many are seasick,” said the group on Twitter.
The Lifeline crew told Euronews they were still stuck at sea with two people under intensive care in the ship’s hospital.
The ship has been at sea for five days now with 250 people on board and is currently off the Maltese coast.
On Tuesday, Italian Prime Minister Giuseppe Conte said the rescue ship would be able to dock in Malta after speaking on the phone with Maltese Prime Minister Joseph Muscat.
"Italy will do its part and welcome a portion of the migrants who are on board Lifeline in the hope that other European countries do the same," he said.
French President Emmanuel Macron promised to take in some of the migrants from the ship.
"For the last few days we've worked on a European joint solution, and I want to salute here the spirit of responsibility of Maltese PM Joseph Muscat," he said.
"With a few others, France among them, he's forged a solidarity, and I can confirm that France, with some other EU member states, will take up people who are on Lifeline now, when they disembark in a European port, and the French Office for Protection of Refugees is already en route towards Malta to get on with this mission".
But the Lifeline crew told Euronews that they had not been contacted directly by any government official.
Earlier this week the Danish cargo ship Alexander Maersk was allowed to dock on the Italian port of Pozzallo in Sicily after rescuing over 100 migrants off the Libyan coast.
Last weekend, EU leaders failed to adopt a unified position to tackle migration and will try again at this week’s summit.
The immigration issue has divided European governments amid a surge in anti-immigrant and far-right political movements in the continent.