48 people have been confirmed dead after the incident.
About 320 people were on board two Yemeni boats traveling via the so-called "eastern route" across the Red Sea, a common route among migrants from the Horn of Africa.
According to the UN's migration agency IOM, the migrants were "forced to leave the ship in open water to swim".
Many migrants try to leave the Horn of Africa to escape conflicts, natural disasters, and difficult economic conditions.
According to IOM, the passengers on the two boats came from Ethiopia and were on their way home from Yemen. Many migrants who make it to war-torn Yemen are unable to continue on to the richer neighboring countries – and therefore return home.
Djibouti's coastguard continued the search late on Wednesday.
