The Vietnamese government is under pressure to take decisive action as the scale of the environmental disaster off the central coast becomes apparent.
Tonnes of dead fish have washed up on hundreds of kilometres of coastline, from Ha Tinh to Hue, after what is suspected to have been a mass leak of toxic chemicals from an industrial plant.
The government has yet to determine the cause of the contamination but says it expects to come up with an answer by the end of the week.
Concern is growing for the welfare of fishermen who depend on the daily catch for their livelihood.
There are fears that some desperate fishermen could sell on contaminated fish because they have no other means of making an income.
The deputy prime minister, Trinh Dinh Dung, said Vietnam may need international help and expertise to determine the source of the leak.
He also acknowledged that the authorities could have responded more quickly to the initial reports that tens of thousands of fish in offshore fish farms were dying, according to a report in the Thanh Nien newspaper.
He said that officials could not have anticipated the unprecedented scale of the disaster.
“The government must come up with an emergency plan to assist the fishermen in the affected provinces because they are literally starving,” said an activist lawyer, Trinh Huu Long, who is trying to organise support from civil society organisations.
“Once they become desperate they are likely to resort to illegal means to feed themselves if they don’t get any help, ” he said.
One social activist at the scene, Nguyen Anh Tuan, said it was also necessary to help the fishermen gather data about their losses so that they would be able to make legal claims for compensation.
The extent of the contamination is threatening to have a damaging knock-on effect.
“Consumers have to be told which areas are safe to eat fish. At this rate, if the majority of the population in Vietnam refuses to eat fish and seafood, our fishermen all over the country will suffer irreparable harm,” said one blogger , Nguyen Thao Chi, reflecting the concern that is spreading across the country.
Another said the disaster showed the urgent need for independent trade unions so that fishermen, as well as other workers and farmers, would have some means to protect themselves and work together at such times of crisis.
Vietnamese state media said that suspicion had focused so far on a steel plant in the Vung Ang Economic Zone run by the Taiwanese company, Formosa Ha Tinh Steel Corporation.
“The substance killing fish could be biological, chemical or anything else. It can also be toxic substances like cyanide,” said the deputy minister of agriculture and rural Development, Vu Van Tam.
The Vietnam Environment Administration said that the steel company had recently cleaned its sewage pipes with toxic chemicals.
However, officials say it is not known whether the cleaning had caused the contamination.
A spokesman for Formosa Ha Tinh told the BBC that the company had recently invested $45 million in a wastewater treatment system and fully met standards required by the Vietnamese authorities.