Some 180 young Ethiopian and Somali migrants, many weakened by hunger and drought in their home countries, were forced from a boat into rough seas off Yemen by smugglers on Thursday and 55 were presumed to have drowned, the U.N. migration agency said.

It was the second such incident in as many days off Shabwa province in southern Yemen, where 50 teenage African migrants were "deliberately drowned" on Wednesday by a smuggler who forced 120 passengers off his boat, the International Organization for Migration (IOM) said.

Smugglers were pushing migrants into the sea away from the mainland so as to avoid encountering possibly armed groups on shore in the war-torn country. They were then going back to pick up more migrants.

"We have seen five bodies and can confirm five dead ... Fifty are still missing from this incident, so 55 are presumed dead," IOM spokeswoman Olivia Headon told Reuters.

"It may be the start of a new trend, smugglers know the situation is dangerous for them and they could be shot at, so they drop them near the shore and turn around and get more," she said.

IOM officials spoke to 25 of the latest survivors, many in need of medical assistance and counselling support, she said.

"These people are really thin. There is an ongoing drought situation in Somalia and Ethiopia. Some may not have had much strength to make it alive to the shore," she added.

The migrants reported that 100 other survivors had already left the beach.

Already this year 55,000 migrants have taken the hazardous route from the Horn of Africa to Yemen to seek possible opportunities offered in the Gulf, IOM said.

Yemen itself is riven by a two-year civil war in which forces loyal to the Saudi-backed government are pitted against Iranian-backed Houthi rebels.