Farmers in Zambia have filed an $80bn (£58.5bn) lawsuit against two Chinese-linked firms, blaming them for an "ecological catastrophe" caused by the collapse of a dam that stored waste from copper mining.

Million of litres of highly acidic material spilled into waterways in February, leading to "mass fatalities" among fish, making water undrinkable and destroying crops, the farmers said in court papers.

This is one of the biggest environmental lawsuits in Zambia's history, with the farmers saying the spillage affects about 300,000 households in the copper-mining region.

The US embassy issued a health alert in August, raising concerns of "widespread contamination of water and soil" in the area.

The lawsuit pits villagers, who are mostly subsistence farmers, against Sino Metals Leach Zambia and NFC Africa Mining, which are subsidiaries of Chinese state-owned firms.

A group of 176 of them have filed papers on behalf of their community in the High Court in Zambia's capital, Lusaka.

They alleged the collapse of the tailings dam - owned by Sino Metals Leach Zambia but located in the surface area of NFC Africa Mining - was caused by numerous factors, including engineering failures, construction flaws and operational mismanagement.

The firms have not yet commented on the lawsuit, but Sino Metals Leach Zambia has previously said there was a spillage of about 50,000 cubic metres.

"The tailings release and breach was promptly brought under control within hours of detection," the firm said in a statement on 3 September.

In the court papers the farmers said they had learned that the water was highly toxic only several days after the tailings dam had collapsed.

It had put the community's health at risk, with people reporting various symptoms of illnesses, including blood in urine and chest tightness, the papers said.

Most villages had dug wells, but even they were polluted and crops had to be burned because they were unsafe for consumption, the petitioners said.

They demanded that the two firms should put $80bn in a Zambian government-managed account as "security" for, among others, "environmental reparation" and "full compensation".

An emergency fund of $20m should also be set up to provide "immediate and urgent" help to people affected by the disaster, and to carry out thorough health and environmental assessments, the petitioners said.

Last month, the US embassy said it had ordered the immediate withdrawal of its personnel from Kitwe - the biggest city in the Copperbelt region - and nearby areas after expressing concern that beyond the "contaminated water and soil, contaminants from the spilled mine tailings may also become airborne, posing a health threat if inhaled".

In response, Zambian government spokesperson Cornelius Mweetwa had said there were no longer any serious implications for public health, and there was "no need to press the 'panic button' today to alarm the nation and the international community".