International aid agencies, including the World Health Organization and the US Centers for Disease Control and Prevention, are assisting Nigerian authorities in containing the outbreak in four villages in Zamfara state.

"We have a total of 355 cases and 163 deaths," Dr Henry Akpan, the health ministry's chief epidemiologist, told Reuters.

"They were digging for gold, but the areas also have large concentrations of lead."

Akpan said many of the victims died after touching tools, soil and water contaminated with large concentrations of lead.

Authorities have stopped the illegal mining and have begun evacuating some residents.