A rubber boat packed with nearly 150 migrants sank in the Mediterranean and the presumed sole survivor - a 16-year-old Gambian boy - told rescuers he believed all other passengers drowned.

A humanitarian vessel, the Iuventa, found the boy hanging onto a fuel tank in the sea on Tuesday. He was transferred first to an Italian Coast Guard ship, then to a Spanish frigate and brought to the Sicilian island of Lampedusa early on Wednesday.

"He said that everyone else died. But there's some hope that the Italian Coast Guard picked up others," said International Migration Organization (IOM) spokesman Flavio Di Giacomo in Rome, after speaking to staff in Lampedusa. 

Hundreds feared dead in the Mediterranean Sea

It should become clear on Thursday whether others survived, as a Coast Guard vessel disembarks migrants in eastern Sicily that day, he said.

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"The boy said they left Sabratha, Libya, a couple days ago on a rubber boat with 147 sub-Saharan Africans on board, including five children and some pregnant women," Di Giacomo said.

He said the boat began taking on water a few hours after setting off, and he survived by holding on to the fuel can. Most of the passengers were from Nigeria, Mali and The Gambia, he said.

In the past two days, rescuers have picked up more than 1,100 migrants at sea, and recovered one body, Italy's Coast Guard said. It did not comment on the latest shipwreck.

So far this year nearly 600 migrants have died trying to reach Italy from North Africa, IOM estimates, after some 4,600 deaths last year. Migrant arrivals to Italy are up more than 50 percent this year on the same period of last year.

Early on Wednesday the Golfo Azzurro, a humanitarian vessel, rescued about 400 migrants - mainly from Morocco, Algeria, Libya, Gambia and Bangladesh - including 16 women and two children.

6,000 people rescued from the Mediterranean

They were found drifting in a wooden boat without power about 16km off the coast of Sabratha, the most frequently used departure point currently used by people smugglers in Libya.

"The migrants kissed and hugged their rescuers and sang songs" after they were brought to safety, said Reuters photographer Yannis Behrakis, who is onboard the Golfo Azzurro.

"My brother back home convinced me to make the trip," said Gambian Kalifa Kujabi, 17, after the rescue. He said he played for Gambia's football academy and paid $600 for the passage.

"My brother said that I can only have a future as a soccer player in Europe."

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Source: News agencies