HANOI (Reuters) - Hundreds of Vietnamese fishermen traveled to a small provincial court on Monday to sue one of the country’s biggest investors for compensation over an accident at its $10.6-billion steel plant, activists and a court official said.

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Tens of millions of fish died in April, in one of Vietnam’s biggest environmental disasters, which the government blamed on a discharge of toxic waste into the sea by Formosa Ha Tinh Steel, a subsidiary of Taiwan’s Formosa Plastics.

Formosa Ha Tinh Steel has promised $500 million in compensation and admitted its steel plant caused massive fish deaths along a 200-km (120-mile) stretch of coastline.

A total of 545 people are suing the company, Dang Huu Nam, a priest leading the group that journeyed 200 km (120 miles) by bus to a town in the central province of Ha Tinh told Reuters in a text message.

“The court is receiving their files,” an official at the Ky Anh People’s Court said by telephone. “It is very crowded here.”

In a video posted on social media site Facebook, Nam said fishermen still feared the sea was polluted and were suffering hardship.

“They cannot go to sea and cannot catch fish while they face the prospect of hunger because of bank debts,” he added.

The disaster unleashed a public outcry on social media and on the streets of big cities. Demonstrators vented their fury at both the government and Formosa, accusing them of a cover-up.

Such protests have been a headache for the authorities, who have accused anti-government groups of trying to exploit the disaster and stir up anger, with the aim of overthrowing the ruling Communist Party.

Monday’s mass lawsuit captured attention on Facebook but was not covered by state-run media.

Activists said Monday’s convoy of more than 10 buses was closely monitored by police, with military also deployed around Formosa’s project in Ha Tinh.

Several thousand Christians gathered around the court and sang songs in support of the fishermen, the priest said, adding that the court was only able to process half the lawsuits filed but would receive more on Tuesday.

Formosa is one of Taiwan’s biggest conglomerates. Its listed units include Formosa Plastics Corp and Formosa Chemicals & Fiber Corp.