A heavily-pregnant Nigerian woman and her husband were evacuated to Malta from the NGO migrant rescue ship Ocean Viking on Wednesday after the woman developed complications.

The evacuation was conducted by AFM helicopter.

The Ocean Viking, operated by SOS Mediterranee, is seeking a safe harbour for another 82 migrants on board.

It said the Libyan maritime authorities have assigned it a port where it could disembark the migrants but it did not consider Libya as being a place of safety.

"We have requested an alternative that meets the requirements of international law," the NGO said.

Some of the migrants, including 12 children, were rescued off the Libyan coast on Sunday, while 34 were transferred to the ship from the sailboat Josefa in a heavy storm on Monday night, some 60 nautical miles off the Libyan coast.

The Ocean Viking, formerly the Aquarius, has a history of being stranded in the middle of the Mediterranean while countries squabble over who should take in the migrants.

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The most recent episode was late last month, when the ship was eventually allowed to transfer 356 migrants to Malta for distribution among six EU countries. Most are still here, putting pressure on the reception facilities.

On Tuesday, five migrants rescued by another ship, the Alan Kurdi, were also brought to Malta for transfer to other countries. That followed another standoff, during which eight migrants were brought to the ship from Malta for medical reasons. 

The government has said it will be beefing up the facilities in view of the crisis.