Around 100 people were missing, feared drowned, in the Mediterranean after a migrant dinghy capsized off Libya on Tuesday, according to NGO rescue teams helping with the search for survivors.

German NGO Jugend Rettet said in a tweet that 23 survivors had been rescued by an oil tanker and that "the crews are searching for survivors in the water and recovering dead bodies".

The survivors and four recovered corpses were transferred from the tanker to the Acquarius, a boat operated by another charity group, SOS Mediterranee.

A survivor told one of the organisation's staff that the dinghy had begun to sink at 6.00 a.m., four hours before the tanker arrived.

"We were 122 on the boat, no children under 15, but there were 10 women travelling with us and only one survived," the survivor was quoted as saying.

"We waited in the water, taking any floating thing to remain afloat, but most of the people drowned, including my little brother. He was 15.

"At 10 the tanker came and rescued us. I want to call home to tell them that my brother died."

The latest tragedy in the Mediterranean came the day after another incident in which it is feared dozens may have drowned after the sinking of another dinghy, from which there were only 15 survivors.