Women and children are among at least 42 Somali refugees who died after their boat was fired at from a helicopter in Yemen, the International Organisation for Migration says.
About 80 survivors were rescued and taken to hospital, according to the IOM.
It remained unclear who had carried out the attack or whether it came from a military vessel or an attack helicopter.
Among the dead on the boat were Somali refugees carrying identity documents issued by the UNHCR, the UN's refugee agency said.
Images from the scene showed the vessel, which was near the Bab al-Mandeb strait, strewn with bodies.
A coastguard in the port of Hudaydah - which is controlled by Houthi rebels - told Reuters the boat had been hit by fire from helicopter gunships.
The rebel-controlled Saba news agency said the refugees had been attacked from the air by the Saudi-led coalition fighting the rebels in Yemen's two-year war.
But an official from the port told AFP news agency the craft had docked and the dead and injured had been hit with light weapons fire.
The coalition, which in general controls Yemen's airspace, has not commented on the incident.
It is also not known where the boat was travelling to and from.
The official said that dozens of Somalis who survived, as well as three Yemeni traffickers, were taken to the city's prison.
In a separate incident on Friday, at least 22 people died in an attack on a mosque inside a military base in Yemen.
Two missiles were fired at the mosque, in the Kofal military camp west of Marib, officials said.
Despite the humanitarian crisis which has brought Yemen to the brink of famine, some migrants from Africa continue to travel to the war-torn country.
UNHCR officials said the people in the boat may have been heading towards Sudan or other countries to the north to escape deteriorating conditions in Yemen.
Somalia is also currently at risk of famine, according to the UN, with 2.9m facing food insecurity - following decades of civil war and a previous famine in 2011.