About 100 migrants are feared to have drowned after being thrown overboard by smugglers in the Gulf of Aden, the UN refugee agency says.
The migrants were attempting to flee to Yemen from war-torn Somalia but were forced off the boat about 5km (3 miles) from the coast, a UN official said.
About 47 migrants managed to swim to shore and alert the authorities.
The UN says about 32,000 people have made the perilous crossing to Yemen this year, and 365 have gone missing.
The boat had left Marera in Somalia, close to the port of Bossasso, on Monday with 150 people on board, according to Ron Redmond, a spokesman for UN High Commission for Refugees (UNHCR).
"The smugglers started beating them with clubs, bars and gun butts"
"Survivors said they counted a total of 47 people reaching the beach and later saw Yemeni authorities burying five bodies," Mr Redmond said at a press conference.
Hussien Hajji Ahmed, a Somali diplomat in Aden, says that some of the survivors who are in a critical condition have been transferred to the UN refugee medical centre in Ahwar.
"The survivors told the rescuers that they were ordered to jump into sea... when they refused, then the smugglers started beating them with clubs, bars and gun butts," he told the BBC Somali Service.
"The people had little chance - either they had to die in the hands of the smugglers or the sea."
UNHCR estimates that in addition to those missing, at least 230 people have died attempting the crossing this year.
Piracy rife
This accident comes a few days after another boat carrying Somali migrants capsized off the coast of Yemen killing at least 30 people.
"I lost three cousins in the accident - two women in their early twenties and a young man," Abdi Weli Ahmed, who survived that shipwreck, told the BBC.
"I recovered the bodies of the two women, but the young man is still missing. I have just buried them. One girl has survived and another family of five."
Last month, the UN refugee agency said that despite the burden on the Yemeni authorities, they were still maintaining an open door policy towards refugees.
But they said that global action was needed to tackle the problem.
Piracy is also rife in the busy shipping lanes of the Somali coast, where dozens of ships have been hijacked this year.
The Nato military alliance has said it will send warships to combat the piracy and help escort aid deliveries off Somalia by the end of the year.
Somalia has experienced almost constant civil conflict since the collapse of Mohamed Siad Barre's regime in January 1991.
Islamist militants are currently fighting government and Ethiopian troops, with frequent bombings and shelling in the capital, Mogadishu
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