A Hungarian court on Monday ordered a retrial of 15 employees at an alumina plant who were cleared last year of criminal wrongdoing over the country's worst toxic spill in 2010.

The court overturned the January 2016 acquittals of Zoltan Bakonyi, the former director of the MAL alumina plant in the western town of Ajka, and 14 employees.

Prosecutors had appealed the original verdict, arguing that judges had committed procedural irregularities and that the disaster could have been prevented if MAL's management had intervened in time.

The deadly disaster occurred on October 4, 2010, after the plant's holding reservoir burst its walls, sending 1.1 million cubic metres (38.8 million cubic feet) of poisonous red sludge into villages in western Hungary.

Ten people died and 150 were injured, many with horrendous chemical burns.

The mud -- a caustic byproduct of producing alumina, which is used to make aluminium -- also wiped out almost all life in nearby rivers, and even spread to the Danube.

After a 40-month trial, the 15 employees were cleared of negligence, waste management violations and damage to the environment, sparking an outcry from victims of the spill.

Prosecutors had demanded prison sentences for all the accused, but the court found that the disaster had been caused by a "loss of stability in the undersoil".

The fault lay with the designers of the reservoir and the authorities responsible for carrying out checks, rather than the company's staff, the court said.

Monday's ruling by a court in Gyor, which lies north of Ajka, is not subject to appeal.

Despite vast sums spent on depolluting the region, it still bears traces of the tragedy.

Hundreds of hectares of land remain sealed off and cannot be used for cultivation.