At least eight people are dead and 22 are missing after two boats carrying migrants ran into trouble in separate incidents over the weekend off the coast of Yemen, says the United Nations refugee agency.

On Sunday afternoon, a boat carrying 23 passengers hit rough seas in the Gulf of Aden about 75 kilometres east of the Yemeni town of Mayfa'a, said the office of the UN High Commissioner for Refugees said Tuesday. While 13 managed to make it to shore, survivors said eight were killed and two are missing.

The vessel had departed from the Somali town of Elayo, according to survivors.

"Witnesses said some of the deaths were due to suffocation after the smugglers covered the passenger area with a tarpaulin to prevent water from getting in," said William Spindler, spokesman for the Geneva-based UNHCR.

On Saturday, a boat carrying 40 Somalis capsized as passengers were disembarking about 80 kilometres east of Mayfa'a, said the UNHCR.

While 20 of those people made it to shore, the rest are missing, said Spindler.

The smugglers who take people across the Gulf of Aden between Somalia and Yemen are notorious for their ruthlessness, such as throwing passengers into shark-infested waters and beating people to death, he said.

More than 17,000 people from the Horn of Africa have arrived in Yemen since the start of the year, Spindler said. Most of them are fleeing violence and poverty in Somalia, he added.

With files from the Associated Press