The spill occurred in February when a waste storage facility burst near the town of Kitwe, in the heart of Zambia's copper belt, releasing millions of litres of acidic mining residue into the environment.

Around 50 farmers, backed by three non-governmental organisations, filed the suit in a Zambian court on Tuesday against the Chinese state-owned Sino-Metals Leach (SML) firm.

They are seeking $220 million in damages to cover environmental and health impacts as well as relocation costs, the court documents said.

According to the applicants, citing "results from independent studies", more than two million square metres of land was visibly contaminated with an average residue depth of 0.3 metres (1 foot).

They also accuse the company of attaching liability waiver clauses to its compensation agreements, which they say effectively prevent affected residents -- most of whom are illiterate -- from seeking further legal recourse.

The new case follows another by almost 200 people affected by the spill who are demanding $80 billion from SML.

They said the exposure to the population had caused a range of health issues including abdominal pains to skin irritations, respiratory issues, vomiting and blood in urine.

SML's holding company, China Nonferrous Mining (CNMC), last week rejected the claims and called the lawsuit "clearly unfounded".

"SML has fully fulfilled its restoration and remediation obligations in accordance with government directives and has completed compensation to individual farmers as per the damage compensation report issued by the Zambian government," it said in a statement.

According to SML, about 50 million litres of waste had been spilled at the site of the incident, but a pollution control company said the amount was about 20 times greater.

The company, Drizit, had been hired through a government tender to assess the damage and clean up the environment, but its contract was drawn up with Sino-Metals Leach. The contract was terminated a day before the final report was due.