Almost 200 migrants believed to be from Pakistan and Sri Lanka have reached Spain's Canary Islands by boat.
Some of the Asians needed medical treatment
They were found to be tightly packed in the hold of the large steel vessel.
Eighteen of them were allowed off the boat for medical reasons. Some said they had been without food or drink for five days.
Spain plans to repatriate the migrants, who are the first Asians among more than 24,000 migrants to arrive on the Canary Islands from Africa this year.
The boat was boarded by Spanish police on Thursday when it anchored 3km (two miles) south of Tenerife island.
The steel-hulled vessel, described by an official as "half-fishing boat, half freighter", was escorted into the port of Santa Cruz on Friday.
The authorities have kept the passengers on board, allowing only 18 of them to go ashore for health reasons. They were treated by the Red Cross and two were taken to a hospital.
The Asians were tightly packed into the hold of the boat. A regional official, Jose Segura, said the conditions aboard were "indescribable".
It is not clear where the migrants had started their sea journey and what their final destination was.
The boat was not flying a flag when the naval patrol went on board.
The crew had mixed with the migrants on board
"There was no one on the bridge and the people who had acted as crew were hiding among the rest of the passengers," Mr Segura said.
Spain's El Pais newspaper says Pakistanis had flown to Dakar, the capital of Senegal, and were paying $500 (£266) each to Senegalese traffickers in the hope of continuing their journey by sea to Greece.
The Asians arrived as Spain resumed repatriation of Senegalese illegal migrants from the Canary Islands. The island authorities say the influx of Africans is a humanitarian crisis.
A special ministerial committee was set up to deal with the arrival of the Asian migrants.
Deputy Prime Minister Maria Teresa Fernandez de la Vega said the government was going to negotiate a fast repatriation of the new arrivals.