At least 139 migrants died, including 15 children, and 84 went missing when an overcrowded boat sank while heading from Djibouti to Yemen, a UN agency said Sunday.

The vessel was carrying 305 people, most of them Ethiopian, when it capsized north of the Djibouti town of Obock on the night of October 8-9, the International Organisation for Migration (IOM) said in a statement.

"Survivors told me that the boat started to sink backwards as soon as they got in it," Alexandre Coissac, IOM chief of mission in Djibouti, told AFP.

"This is a devastating loss of life," he said earlier in the statement.

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"Our thoughts are with the survivors and the families who have lost loved ones or remain without news of their relatives."

The IOM gave an initial toll of 109 dead and 116 missing, and revised it to 139 dead and 84 missing in a later statement after more bodies were recovered.

Coissac said IOM teams were on the ground alongside Djiboutian authorities to provide emergency aid.

"This tragedy is a stark reminder of the dangers faced by migrants along this migration corridor as they seek economic opportunities" by trying to cross the Bab al-Mandeb Strait to Yemen and then reach Gulf countries, he said.

Coissac said he had spoken to one survivor of the wreck who came from the Tigray region of northern Ethiopia, where rebels are battling the federal government in a recent flare-up of violence.

Among the 109 bodies earlier recovered were 52 men, 42 women and 15 children - nine girls and six boys - the initial statement said.

Eighty-two people survived the shipwreck, all Ethiopian nationals, according to the updated toll.

"Poverty, insecurity and the growing impacts of climate change drive many to undertake this journey, despite mounting instability across the Middle East," the IOM said.