"As at 12th May, 2015, 65 cases and 28 deaths had occurred giving a case fatality rate of 43 per cent," junior health minister Fidelis Nwankwo told reporters in Abuja.
"All the 28 cases were children below the age of five."
The victims of the poisoning -- suspected to be due to illegal gold mining -- were found to have levels of lead in their blood which were 17 to 22 times higher than the minimum international standards.
Animals and livestocks were also affected by the outbreak, Nwankwo explained, adding that sick children were being treated.
In 2010 lead poisoning in northwestern Zamfara state, which borders Niger state to the north, killed at least 400 children, with some 2,000 more affected.
The French aid group Doctors Without Borders (MSF) described the incident as "the worst outbreak ever recorded".
Lead was dispersed in several areas by the processing of ore for gold extraction using unsafe mining techniques.
Local communities had initially largely concealed or denied the fatalities and illnesses from lead poisoning, fearing the authorities would ban their mining activities.
The short-term effects of lead poisoning include acute fever, convulsions, loss of consciousness and blindness, with anaemia, kidney failure and brain damage among the long-term effects.
