Experts say Africa will struggle to control the deadly H5N1 strain of bird flu, which was discovered in poultry in northern Nigeria.
Nigerian Agriculture Minister Amadu Bello said chickens at a farm in Jaji, in the state of Kaduna, have been dying of the disease for the past month, however officials at first mistook the cause to be a bacterial infection known as bird cholera.
A team of experts were sent to the affected farm after a United Nations laboratory in Italy confirmed it was the H5N1 strain, and culling procedures have been launched.
Authorities say they have also disinfected the affected farm, imposed a quarantine and restricted animal movements.
"The outbreak in Kaduna state in northern Nigeria proves that no country is risk-free and that we are facing a serious international crisis," said Samuel Jutzi, head of UN Food and Agriculture Organisation's animal health division.
"If the situation in Nigeria gets out of control, it will have a devastating impact on the poultry population in the region," he told reporters in Rome.
He said the virus would seriously disrupt the livelihoods of millions of people and increase the exposure of humans to the virus.
Millions of people in Nigeria rear chickens as a basic source of income.
But traders in Kano, northern Nigeria's main commercial centre, said that similar mystery disease outbreaks have been reported across the region and that farmers are rushing sick birds to market in order to avoid a blockade.
Farmers are reportedly planning to hold an emergency meeting in Kano, and will discuss the plummeting price of chickens.
The World Health Organisation said it is "very concerned" about the outbreak.
Nigeria has banned poultry imports from countries that have had bird flu, and South Africa and Mauritania have now become the first to ban Nigerian imports.
There are fears that a lack of safeguards, combined with Africa's rundown public health infrastructure, will hamper efforts to stem the rise of the virus.
"This is a worrying development ... It means that the disease has got a foothold on the continent," Jean-Luc Angot, deputy director general of the World Organisation for Animal Health (OIE), told AFP.
"Africa doesn't have sufficient infrastructure for veterinary surveillance and control. We think that other countries will be affected," he warned.
A Kenyan health official said the threat is serious, particularly as east African countries are threatened by migratory birds bringing the flu in.
"People are malnourished and their immune systems are down. Also, with the high rates of HIV/AIDS infection, this has the potential to be a catastrophe," warned Phillip Muthoka.
A team of FAO experts is due to leave for Nigeria on Thursday.
Bird flu spreads rapidly among poultry and wild birds, including migratory species, and can be transmitted to humans through physical contact with sick animals.
Health experts fear that the virus could, however, mutate through contact with the human influenza virus and therefore become transmissible through human-to-human contact, triggering a deadly worldwide epidemic.