(CNN) Up to 150 people have drowned after their boat sank off the Libyan coast Thursday, the UN Refugee Agency (UNHCR) confirmed.

Around 300 people are believed to have embarked on the dangerous sea crossing from the Libyan port city of Al-Khums, 80 miles east of Tripoli, UNHCR spokesman Charlie Yaxley said.

The vessel got into trouble in the waters off the coast of Libya. Some passengers were rescued by local fisherman, who were later joined by the Libyan coastguard, he added.

Rescued migrants sit on a coast some 100 kilometers east of Tripoli, Libya, Thursday.

"More than 600 people have now lost their life on the Mediterranean Sea this year," Yaxley said. "If current trends continue, we are likely to see more than a thousand people lose their life on the Mediterranean for the sixth year in a row, which is a bleak milestone for us to be reaching."

The Libyan branch of the International Organization for Migration (IOM) also tweeted on the incident, posting that 145 were rescued.

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