The government has rejected reports that pollution remained after the tailings dam wall at the copper mine burst and released acidic waste into streams and rivers near the town of Kitwe, about 285 kilometres (180 miles) north of the capital Lusaka, in February.

The pollution "killed fish, burned maize and groundnut crops, and led to the deaths of livestock, wiping out livelihoods of local farmers and posing harm to residents," Human Rights Watch said in a statement.

"Zambian authorities should conduct a comprehensive investigation with international and domestic experts to identify environmental health risks, and test affected communities for possible acute and cumulative heavy metal poisoning," it said.

Zambia's environment minister on Wednesday dismissed findings by South African pollution control company Drizit that estimated around 1.5 million tonnes of waste was spilled, far greater than the 50,000 tonnes announced by the Chinese company, Sino-Metals Leach.

Acting minister Collins Nzovu warned against "peddling falsehoods on such a sensitive matter".

Drizit was selected by the Zambian Environmental Management Agency (ZEMA) to assess the damage and clean up the environment.

But "after submitting reports indicating the severity of the pollution and associated risks to communities and the environment, Sino Metals terminated the contract one day before the final report was due," the company said in a statement on August 29.

Drizit said their studies found the waste contained "dangerous levels of cyanide, arsenic, copper, zinc, lead, chromium, cadmium, and other pollutants posing significant long-term health risks, including organ damage, birth defects, and cancer."

ZEMA was due to select another clean-up company by Monday, the minister said.

Last month, the US and Finnish governments urged their citizens to avoid travelling in areas affected by the pollution.