Nigeria announced Wednesday that the H5N1 strain of avian influenza -- which can be fatal to humans -- had been found in Sambawa Farm near Kaduna, 300km north of Abuja.

But Auwalu Haruna, secretary of the Kano State poultry farmers' association, said that a similar infection, identified earlier as "fowl cholera", has been spreading through flocks further north for the past two weeks.

"The disease is spreading like wildfire," he told AFP.

"We have 20,000 new infections reported today, bringing the figure for infected birds to 80,000. What worsens the situation is the farmers' movement of infected poultry, in a frantic effort to minimise losses," he said.

Haruna and several market stall holders told AFP that once chickens are seen to be infected, farmers are killing them and rapidly dumping the on the market in an effort to beat any future quarantine and make a quick profit.

"The announcement by the federal government of bird flu at Sambawa Farm shocked us, but we are just waiting for confirmation from the veterinary institute in Vom for our birds," Haruna said.

International experts from the UN Food and Agriculture Organisation were expected to arrive in Nigeria on Thursday and the agriculture ministry has promised a large-scale operation to quarantine farms and destroy sick birds.