The Philippines will cull 200,000 chickens, quails and ducks after confirming the country's first outbreak of bird flu, Agriculture Secretary Emmanuel Pinol said on Friday.

The avian flu outbreak was detected in a farm in San Luis municipality in Pampanga province, north of the capital Manila, which later spread to five neighbouring farms. There has been no case of human transmission although health officials are conducting checks on farm workers.

"We have declared a 1-km (0.6 mile) quarantine radius with the epicentre being San Luis. All fowls found within the area will be culled and buried, and the estimated population is 200,000," Pinol told reporters at a news conference.

"That would include every bird, every duck, every quail, every poultry within the vicinity of the quarantine area."

The volume of birds to be culled was half of Pinol's initial estimate of 400,000, which he said was based on a preliminary evaluation and was later revised after inspection.

Initial tests ruled out the highly pathogenic H5N1 as the virus strain, Dr. Celia Carlos told reporters, and samples will be sent to Australia for further testing.

"The Department of Health is doing surveillance of possible human cases especially concentrating on people who have been exposed to the affected animals or poultry," Carlos said.

Culling should be completed within the next three days, said Pinol. The virus may have come from migratory birds from China or smuggled ducks, also from China, he said.

There were indications as early as April of bird flu hitting one farm, but the situation worsened in July, with around 37,000 birds dying during the period, Pinol said.

He said he had informed President Rodrigo Duterte of the outbreak and a report would be submitted to the Paris-based World Organisation for Animal Health.

The Philippines is the latest country in Asia, Europe and Africa where the bird flu viruses have spread in recent months. Many strains only infect birds, but the H7N9 strain has led to human cases, including fatalities, in China.