At least 13 people in northern Zambia have been admitted to hospital after drinking water alleged to have been contaminated by a nearby mine.
In 2006, the town of Chingola was affected by water contamination
Officials from Mufulira, who visited the site, claim acidic effluents from Mopani Copper Mines accidentally entered the water supply on Wednesday.
The BBC's Boyd Kaimbi Chibale says police have deployed in case of riots.
He says the atmosphere is volatile after a similar water contamination affected nearby Chingola in 2006.
Our correspondent in the Copperbelt Province says Mufulira residents, who number about 800,000, are afraid to drink tap water.
They are collecting water from shallow wells or nearby streams.
Farmers fear their crops planted near the Kafue River will be affected.
Mopani Copper Mines said the water used at its plant was treated before re-entering the water system.
Those admitted to hospital in Mufulira, some 40km (25 miles) north of Kitwe, were suffering from abdominal pains, our reporter says.
"Nobody has died but we are screening all the people who consumed the water," Mufulira town official Charles Mwandila said, AFP news agency reports.