Up to 64 migrants died off the coast of Libya at the weekend when their flimsy boat sank, humanitarian groups said on Monday after talking with survivors evacuated to Italy.

Eighty six people were plucked from the stricken rubber dinghy on Saturday and eight bodies, all women, were recovered. However, the boat had been carrying 150 migrants, survivors said, with many of the dead vanishing beneath the waves.

“Among them there were many children who are believed to have drowned at sea,” said Doctors Without Borders Sea on Twitter. “Among the survivors was a three-year-old child who has lost her mother and arrived alone, and a family of 11 now a family of three,” it added.

The Italian coastguard said the migrants had been spotted on Saturday morning by a plane patrolling the seas on behalf of a European anti-smuggling operation. Rescuers believe their dinghy deflated following a puncture.

Such boats are regularly crammed with migrants by people smugglers operating from Libya and were never built to withstand crossing the Mediterranean Sea.

The International Organization for Migration (IOM) estimated that 2,832 migrants died last year trying to reach Italy from North Africa, down from 4,581 in 2016. Some 119,310 people made it alive to Italy in 2017 against 181,436 the year before.

The majority of the migrants are Africans fleeing war and poverty back home. Italy is working with various groups and authorities in Libya to slow the flow of newcomers.