Up to 117 migrants might have died when a rubber dinghy capsized in the Mediterranean off Libya, survivors said.

Flavio Di Giacomo, of the International Organisation for Migration, said three survivors were plucked to safety by an Italian navy helicopter on Friday, and they said 120 were aboard when the dinghy left Libya.

The navy said its plane launched life rafts after it spotted the sinking dinghy with about 20 people on board. It was not clear if some migrants had already fallen off.

The Italian Coast Guard said Libya asked a nearby cargo ship to search for survivors but no one was found.

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A rescue operation was launched after the dinghy capsized off the coast of Libya (Rene Rossignaud/AP)

The Italian news agency ANSA quoted Libyan authorities as saying a Libyan coastguard boat turned back after mechanical problems.

Among the missing are 10 women and two children, including a two-month-old baby, Mr Di Giacomo said. Survivors indicated their fellow migrants came from West African countries, including Nigeria, Ivory Coast and Gambia. Also among the missing are Sudanese migrants, Mr Di Giacomo said.

A navy spokesman said all of the survivors were suffering from hypothermia.

They were flown to Lampedusa, an Italian island near Sicily, and treated in hospital.