At least 30 refugees and migrants have drowned off the coast of Aden, Yemen, after their boat capsized, the United Nations has reported.

The UN's migration and refugee agencies said on Friday that the boat, overcrowded with at least 152 Somalis and Ethiopians, had departed from the Al Buraiqa coast in Aden on January 23.

The International Organization for Migration (IOM) and UNHCR said the vessel was believed to have been operated by "unscrupulous smugglers" who were trying to bring refugees and migrants to Djibouti "while trying to extort more money from them".

In a statement, the UN said the boat had capsized "amid reports of gunfire being used against the passengers".

Of all passengers on board, 101 were Ethiopian, and 51 were Somali.

"As we have been saying for almost five years now, the preservation of human life is our utmost priority everywhere," IOM Director William Lacy Swing said.

"Yemen is no exception; we are deeply troubled by reports of this latest incident."

The ongoing civil war in Yemen exposes refugees to further human rights abuses, including arbitrary arrest, detention, trafficking and deportation.

So far this year, the IOM has recorded at least 349 migrant fatalities across the world.