The deadly H5N1 strain of bird flu has been found on three more farms in northern Nigeria, where thousands of poultry have died recently.
Nigeria has started culling birds at affected farms
Officials said tests had confirmed bird flu on farms in two different states to where Africa's first case of bird flu was confirmed on Wednesday.
Chickens have been dying in Nigeria for a month, leading to fears that the virus may have spread widely.
The government says it has now imposed a quarantine on the affected farms.
Large-scale culls of poultry have also begun.
The World Health Organization has called for a massive public education campaign, to stop bird flu from spreading to humans in Nigeria.
"The single most important public health priority at this stage is to warn people about the dangers of close contact with sick or dead birds infected with H5N1," a WHO statement said.
Although Nigeria's government has said it will compensate farmers if their poultry are killed, people have been rushing to sell sick or dead chickens in the markets before restrictions are imposed.
Neighbouring Benin, Cameroon, Chad, Ghana and Niger have all banned chicken imports from Nigeria.
The new cases - confirmed by National Veterinary Research Institute head Doctor Lamy Lombar - are in Kano State and Plateau State, on either side of Kaduna, where the first case was found.
Samples have now been sent abroad for further analysis.
Agriculture Minister Adamu Bello met diplomats and UN agencies to appeal for help to contain the outbreak, reports the AFP news agency.
"We told them that we need facilities such as laboratories, vaccines and technical support," he said.
The remaining poultry on the first farm - some 300 ostriches - were shot on Thursday night in a bid to contain the outbreak.
Auwalu Haruna, head of the Kano Poultry Farmers' Association, has accused the authorities of being slow to react to the suspicious deaths of chickens - giving the virus time to spread.
"We have 30 farms that have been affected, and we're still counting... Just yesterday, 40,000 chickens died at Phed Farm alone."
It is not clear how the virus has spread to Nigeria. It was first found in South-East Asia and more recently Turkey and Russia.
Some experts blame illegal poultry imports; others migrating birds.
More than 80 people have died of H5N1 bird flu since the disease's resurgence in December 2003 - most of them in South-East Asia.
Experts point out that cross-infection to humans is still relatively rare, and usually occurs where people have been in close contact with infected birds.
But they say if the H5N1 strain mutates so it can be passed between humans, it could become a global pandemic, killing millions.