HANOI (AFP) - A senior Vietnamese environment official has been fired for negligence over a toxic waste dump that killed tonnes of fish in a major environmental crisis last year, according to officials and state media.

Luong Duy Hanh, director of Vietnam's Environment Protection Management Department, is the latest official to be punished over the toxic leak, which was blamed on a multi-billion dollar steel plant run by the Taiwanese firm Formosa.

Formosa was fined US$500 million (S$695.15 million) for the waste dump and Vietnam has vowed to punish 11 officials over the country's worst-ever environmental disaster.

"The Ministry of Natural Resources and Environment has carried out disciplinary action by sacking Mr Luong Duy Hanh," according to an online statement from Vietnam's environment ministry published on Tuesday (June 20).

State media reported on Wednesday (June 21) that Hanh was sacked because he failed to properly oversee the Formosa project.

He was blamed for not "consulting and supervising the implementation of the environmental protection unit during the construction and pilot operation" of the plant, according to state-controlled Thanh Nien newspaper.

A deputy director of the Environment Agency has already been fired over the mass fish kill, and four former officials have been stripped of their Communist party positions.

The Formosa steel plant was still under construction at the time of the disaster in April 2016.

Last month, the government gave it the green light to operate on a trial basis.

The disaster decimated livelihoods in fishing towns along the central coast, and fishermen continue to stage protests demanding greater compensation.