A shipwreck off the Libyan coast has killed 20 people, Doctors Without Borders said, just hours after news of a separate incident in which at least 74 migrants died.

MSF teams in northwestern coastal city of Sorman "assisted three women as the lone survivors of another shipwreck where 20 people drowned," MSF said.

"Rescued by local fishermen, they were in shock and terrified; they saw loved ones disappear beneath the waves, dying in front of their eyes," it added.

Earlier on Thursday, the UN's International Organization for Migration reported "a devastating shipwreck which claimed the lives of at least 74 migrants off the coast of Khoms," a port city 120 kilometres east of the Libyan capital Tripoli.

It said that 47 survivors had been brought back to shore and 31 bodies retrieved, adding that the boat was reported to be carrying more than 120 people.

The day before, a six-month-old baby was among six asylum seekers who died in another shipwreck.

Footage of his desperate mother, pleading with rescuers to save her baby as they fish out another toddler from the Mediterranean Sea, was uploaded by humanitarian NGO Open Arms

The IOM said that so far this year, at least 900 people had drowned in the Mediterranean trying to reach European shores - some due to delays in rescue.

More than 11,000 others have been returned to Libya, it said, "putting them at risk of facing human rights violations, detention, abuse, trafficking and exploitation".

Human traffickers have taken advantage of persistent violence in Libya since the 2011 overthrow of dictator Moamer Kadhafi, turning the country into a key corridor for migrants fleeing war and poverty in desperate bids to reach Europe.

While many have drowned at sea, thousands have been intercepted by the Libyan coastguard, which has been backed by Italy and the EU, and returned to Libya.

They mostly end up in detention, often in horrific conditions.