Twenty-eight African immigrants were held in slavery on a China-flagged fishing vessel off the coast of Uruguay where they were beaten and forced to work without pay, attorneys said Wednesday.

The migrants, 24 of whom were from Sierra Leone and the rest from Ghana, said they had not been paid "a penny" since boarding the ship seven months ago.

They were initially divided up between three boats but, upon reaching Uruguay's territorial waters, were transferred to a single vessel that docked in Montevideo on Sunday and taken to a hotel.

The name of the boat has not been disclosed.

A complaint was filed late Tuesday.

"It's a case of forced labor," Isabel Camarano, a lawyer with Uruguay's fishermen's union, told reporters.

Camarano said the men, who were taken from port to port as forced labor, were abused. Doctors have confirmed they have wounds and scars consistent with having been beaten, she added.

Local news reports said the men had signed on as contract labor to work on the ship but that the captain confiscated their passports and the crew subsequently held them captive. Most had embarked in Sierra Leone.

The workers told the fishermen's union that "they were beaten aboard the ship. Apart from that, they said that food was withheld from them, and that they have become ill," Camarano said.

Stanley Elisami said he and the other migrants blamed the owner of the vessel for keeping them on board against his will.

"The captain said that no one who gets sick would be allowed to sleep on this ship. Even if you're sick, you had to work," Elisami told reporters.

He said the men were given small rations of rice to eat just once per day and had to resort to drinking ocean water while "the Chinese drank fresh water."

The men have been examined by doctors who said they appeared to have early symptoms of malaria and possibly tuberculosis.

They have been referred to two Uruguayan hospitals for treatment.

The case made it to the authorities by chance and good fortune.

"I found them walking down the street," said Michel Ama, an African who has lived in Uruguay for a decade. He contacted the shipping union and the foreign ministry for help.

"They told me that they had come over on ships, that they were abused, that they were beaten and given very little food. They did not know what to do," Ama added.