Several birds infected with avian influenza have been found in Uusimaa this winter.
The H5N8 virus was detected in sick and injured birds in February and early March this year, including in a swan found dead in Helsinki's Eläintarhanlahti park and a goshawk sent to Korkeasaari Wildlife Hospital from Kumpula.
Helsinki's chief veterinary surgeon Päivi Lahti said the avian flu had also been found in other parts of Uusimaa.
"The disease has also been found in birds in Hanko, Espoo and Tuusula. It seems that there is bird flu across a wide area, at least here in southern Finland," she said.
The situation is very different to that seen during a previous outbreak of the virus, Lahti said.
"It was not previously present in so many different places in Finland. Last time, the disease was limited to southwestern Finland, but there are now several cases around southern Finland. This is now an exceptional situation for us," she said.
Spring migrations likely to spread the outbreak
"There has been quite a lot of the H5N8 virus in birds in Europe. The virus will definitely come along with migratory birds, though the worst-affected will likely die on the journey here," Lahti said.
The first case of H5N8 was detected on a pheasant farm in Janakkala in January. Following that discovery, the Finnish Food Authority instituted a ban on keeping poultry outdoors, effective from 8 February.
"The bird flu virus is not easily transmitted to humans and being infected usually requires close contact with a wild bird, poultry, or their secretions," the authority said in a statement.
However, it was reported in late February that the virus had spread to humans, when seven workers at a poultry plant in southern Russia were infected. Authorities said that the virus was not passed from person to person.