The New Zealand government has decided to list avian influenza, which has caused the potentially dangerous bird flu outbreak in Asia, as a notifiable disease.

"We have made highly pathogenic avian influenza notifiable," Health Minister Annette King said in a statement Tuesday.

The order-in-council was signed Monday and it will be gazetted Wednesday and take effect on Thursday.

The virus causing avian influenza is of the family Orthomyxoviridae, but in poultry this group can be divided into low pathogenic (LPAI) and highly pathogenic (HPAI) forms, said to the minister.

Most bird flu virus strains are low pathogenic forms, but some can mutate into a highly pathogenic virus that is extremely infectious and kills quickly. The virulent viruses can cause 100 percent mortality in poultry.

Several Asian countries have been hit by the outbreaks of the highly pathogenic H5N1 bird flu, said the minister, adding that there have been no cases in New Zealand of bird or human infections.

There has been no record of the virus spreading from human to human so far -- the 19 people killed to date appeared to have been infected by birds.

But it was "prudent" to prepare for the possibility of a human- to-human spread, or for a traveler to New Zealand becoming infected through contact with poultry, King said.

She said "if this virus combines with a human influenza virus, we could have a global epidemic of a new and devastating illness which would be many times worse than severe acute respiratory syndrome (SARS)."

The death rate among humans infected with the H5N1 bird flu has been put at about 70 percent -- mostly young people.