A third outbreak of avian flu has been detected in Washington state, prompting agriculture officials on Tuesday to warn bird owners to keep their flocks away from migratory birds that have spread viruses from Oregon to British Columbia.

State and federal agriculture officials culled about 120 backyard chickens, geese and ducks in Clallam County, 125 miles (200 km) northwest of Seattle, on Sunday after confirmed infections of the highly pathogenic H5N2 strain of avian flu.

"All bird owners, whether commercial producers or backyard enthusiasts, need to continue practicing good biosecurity, preventing contact between their birds and wild birds and reporting sick birds or unusual bird deaths," said U.S. Department of Agriculture spokeswoman Joelle Hayden.

The virus has not been found in commercial poultry and there was no immediate public health concern, federal agriculture officials said.

Most strains of bird flu viruses do not infect humans, although some strains can be dangerous or deadly.

In December, the USDA confirmed two separate virus strains of bird flu in Washington's northern Whatcom County, near the Canadian border, with infections detected in pintail ducks and captive Gyrfalcons that were fed hunter-killed wild birds.

Earlier this month, the Washington State Department of Agriculture imposed an emergency eight-month quarantine of poultry and eggs in parts of Benton and Franklin counties, in the state's southeast, after the H5N2 strain was found in two flocks of mixed poultry there.

The virus is extremely contagious among poultry and can spread rapidly through a flock, killing birds in as little as 48 hours. The H5N2 strain of bird flu has killed thousands of birds on two Canadian farms in British Columbia.

Last week, China banned all imports of U.S. poultry products and eggs following the discovery of avian influenza in the U.S. Pacific Northwest, the USDA said. All poultry shipped to China after Jan. 8 was to be returned or destroyed, the agency said.