Police in Yemen have detained at least 5,000 migrants over the last 10 days who were attempting to cross to Saudi Arabia.
The officials said the migrants, most of them from African countries, are being held in overcrowded police stations across the southern city of Aden.
Aden's security chief, Shalal Shaye, said the migrants have launched a hunger strike.
He said authorities were seeking assistance from the UN migration agency and aid groups.
Migrants from the Horn of Africa continue to travel to Yemen en route to jobs in the oil-rich Gulf despite the four-year war between a Saudi-led coalition and Iran-linked Houthi rebels.