Some of the 49 migrants who have been stranded on the NGO rescue ship Sea Watch for almost three weeks have stopped eating and others are being treated for dehydration, the vessel's captain said on Sunday.

Contacted by radio during a press conference hosted by the German NGO in Valletta, Capt Kim Heaton-Heather said most of the migrants were depressed and the situation was getting more difficult.

While the crew were trying to keep spirits high “there is only so long you can hold bad news”.

During the press conference, Sea Watch spokeswoman Georgia Linardi insisted there was nothing irregular about the manner of rescue of migrants conducted by the NGO.

She was reacting to comments by Prime Minister Joseph Muscat who had cast doubts on the method of rescue during a radio interview earlier in the day.

Sea Watch spokeswoman Georgia Linardi.Sea Watch spokeswoman Georgia Linardi.

Going through the rescue, Ms Linardi told Times of Malta that the migrants had departed from the Libyan port city of Zuwara. A spotter plane found them in a dinghy and the NGO deployed its ship to their location. The 32 migrants were embarked after they were found to be in distress.

Both Malta and Italy have refused permission for Sea Watch to enter harbour, but Malta last week allowed the vessel to enter its waters to shelter from rough seas.

The spokeswoman said the vessel was currently at double its capacity and the rescued asylum seekers were being accommodated in a crowded room. As the boat rocked, the migrants were "throwing up on each other and in very difficult situation”.

She said the NGO had been following the EU-level discussions on burden sharing and could not believe that these human beings were being made to live in such conditions.

“We want to stress we are talking about human beings here. They are aware of their situation and have even asked the captain why member states would not share them,” the spokeswoman said.

Asked how much longer they thought the migrants could stay on board, she said it had already been far too long.

“This is already the worst case scenario,” she said.  

Pope Francis earlier on Sunday appealed to EU governments to offer concrete solidarity to the migrants.