HONG KONG - Aviaries at a popular Hong Kong theme park were closed to the public for three weeks beginning Thursday, after tests indicated that a wild heron found dead in the park may have been killed by bird flu, agriculture officials said.

Authorities found the body of the Black-crowned Night Heron outside an aviary in Ocean Park on Monday, the agriculture department said in a statement.

Preliminary tests indicated the bird may have contracted the H5 virus, and further tests were being carried out to see if it was the deadly H5N1 strain, the statement said.

As a precautionary measure the government said it will close Ocean Park"e;s walk-in aviaries — a 17,000-square-foot canopied area where visitors can walk among the birds — for three weeks. It also is warning poultry farmers to take extra precautions against the disease.

Feces samples from birds kept in the Ocean Park aviaries have tested negative for the H5N1 virus, officials said.

Last year, Hong Kong discovered 21 wild birds infected with H5N1, but it has not suffered a major outbreak of the disease since 1997, when the virus killed six people, prompting the government to slaughter the territory"e;s entire poultry population of about 1.5 million birds.

A number of Asian nations recently have reported fresh outbreaks of the virus in poultry. Experts fear bird flu could mutate into a form easily transmissible among humans and spark a flu pandemic.

At least 223 people have died worldwide from avian flu. Most cases have been linked to contact with infected birds, but scientists believe limited human-to-human transmission has occurred among familiy members who had close contact.