A mysterious discharge of highly toxic chemicals in the Caribbean off the northern coast of Puerto Rico has caused two deaths in the Dominican Republic and poisoned millions of fish in one of the world's richest fishing grounds.

The Dominican government has banned all fishing until further notice, issued nationwide warnings against seafood consumption and seized all fish in markets, shops and restaurants as waves of dead fish continue to wash ashore in that island nation.

Although the dangerous chemicals probably will be diluted over the next several days, there is rising concern that the poisoned waters will be carried northwest toward the Bahamas and the Florida coast, where American and other fishing fleets work important fishing grounds.

Reached by telephone, Dominican authorities said they have already found several unmarked 55-gallon barrels in the area with liquids containing mercury, chlorine, sulphur and phosphates. Because there have been no reports of sea accidents, they said they believe the substances were dumped deliberately.

Navy Capt. Narciso Almonte, director of the Dominican Department of Fisheries, said that on the basis of the currents, the chemicals were believed to have entered the water near the northwestern tip of Puerto Rico.

First evidence of the disaster came last Tuesday when Puerto Rican fishermen found thousands of dead fish floating in the water off their western coast. Vast blankets of dead fish then began to appear on the eastern tip of the Dominican Republic. The currents carried the poisoned waters and dead fish both to the north and south coasts of the island of Hispaniola, which the Dominican Republic shares with Haiti.

Despite immediate government warnings on radio and television in the Dominican Republic, presidential spokesman Franklin Dominguez said that at least two persons have died and more than 90 suffered varying degrees of intoxication.

To trace the cause of the disaster, Dominican officials said they were in touch with their counterparts in Puerto Rico, where fishing was also halted in certain areas. They said they had not discovered any hints of the origins of the chemicals because the barrels they found showed no writing or symbols of any kind.

Capt. Almonte said analysis of the chemicals in the barrels "coincided exactly with the analysis of the water, the dead fish and the seaweed," conducted by his department.

Almonte said in a report that two types of liquid were discovered in the barrels -- "one was very dark, one light. Both were very thick, with a strong smell." Almonte said the government investigation showed that literally "millions of fish" have been killed already by the poison, which can have immediate strong reactions or slow, lasting effects in humans who consume fish or shrimp that survived but absorbed the chemicals.

Government officials could not immediately provide figures of Dominican fish exports to the United States.