CATANIA, Italy (Reuters) - More than 240 migrants died or went missing in the Mediterranean this week, humanitarian groups said on Wednesday, as another 580 people were pulled from overcrowded boats.

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On Monday a rubber boat ripped and flipped over with about 150 on board, U.N. refugee agency spokesman Iosta Ibba quoted some of the 15 survivors as saying when they arrived in Catania on Sicily’s east coast.

“The survivors made it by hanging on to the pieces of the boat that stayed afloat,” Ibba said. “They were in the water for several hours, some said about 10 hours, before an oil tanker picked them up.”

On Tuesday, 23 people were brought to safety by another tanker after a rubber dinghy carrying about 122 deflated, said SOS Mediterranee, which operates rescue ship Aquarius. Four bodies were recovered.

“We waited in the water, grabbing hold of whatever floated, but most people drowned, including my little brother. He was 15 years old,” one survivor in apparent shock told the Aquarius crew.

On Wednesday, one body was picked up, the Italian coastguard said, while 580 were brought to safety. Six other bodies were recovered on Monday and Tuesday, and witnesses saw a man drown without being able to recover the body.

The sea between Libya and Italy has become the most dangerous migrant crossing in the world, with the death toll surging to more than 4,270 this year compared to 3,777 in 2015, the International Organization for Migration says.

“The boats are increasingly unseaworthy, and are always more crowded,” said the U.N.’s Ibba. “Many tragedies are also tied to bad weather.”

Almost 500 migrants arrived at the port of Catania on Wednesday, including those from Monday’s shipwreck, as the influx of refugees heading to Europe showed no signs of abating.

Hundreds of people, mostly men from sub-Saharan Africa, huddled under gray blankets on the deck of the Italian coastguard vessel Diciotti as they started to disembark in pouring rain.

There were a record 27,383 arrivals in Italy in October, according to the Interior Ministry. As of Nov. 16, arrivals were already more than double the same month last year amid worsening sea conditions.

Some 167,000 migrants have reached Italy by boat so far this year, exceeding the total for all of 2015 which stood at 154,000, and quickly approaching 2014’s record of 170,000.

Italy has borne the brunt of new arrivals since the implementation in March of an agreement between Turkey and the European Union for Turkey to curb the flow of migrants and refugees sailing from its shores to reach Greece.