The strange situation first came to light when farmed fish in the area began dying in great numbers, he said, with locals later discovering huge numbers of dead fish on beaches.

Local fishermen told state-run media that they are burying hundreds of kilograms of fish everyday.

“If you sail just three miles offshore, you can see dead fish all over the ocean floor,” the state-run Tuoi Tre quoted local fishermen as saying.

Signs point to the fish having been poisoned by “unidentified substances,” Tran Dinh Du, deputy director of agriculture in Quang Binh province, said, according to the report.

“We have asked people not to eat the fish and not use the fish as food for their livestock,” Du added.

State news outlet Thanh Nien quoted worried locals saying they dared not eat any of the washed up fish, adding in their report that “all signs [are] pointing to an environmental disaster.”

Central Ha Tinh province is home to a sprawling economic zone which houses numerous industrial plants, including a multi-billion dollar steel plant run by Taiwanese conglomerate Formosa.

Hanoi has dispatched teams of environmental experts and officials to investigate the phenomenon, the Ministry of Environment said in a statement posted online.

“We must quickly establish whether the fish have died because of environmental pollution,” Environment Minister Tran Hong Ha said in the report.

Vietnam has a long coastline and much of the country’s export income depends on seafood, including farmed shrimp, catfish and wild-caught tuna.

Last year, the country earned US$6.6 billion from seafood exports.