A slaughter of nearly all poultry in Hong Kong is in full swing as the authorities try to prevent an outbreak of avian flu.

Up to 1.2 million chickens and other birds are being killed in order to wipe out the influenza virus in the territory in case it becomes a threat to humans.

It was a necessary decision to protect the health of our citizens Tung Chee-hwa HK chief executive

Further measures in force include territory-wide chemical cleansing of poultry market stalls, and a ban on poultry imports from the rest of China.

Officials stress that the virus does not affect humans, unlike the strain in the 1997 outbreak, which killed six people.

The slaughter is expected to last up to three weeks and cost an estimated $10m.

Efforts are continuing to trace the source of the current outbreak.

Birds are being killed by carbon dioxide, bagged and dumped in landfill. Some 40,000 will be dispatched in the wholesale market on Saturday alone.

Neighbouring Macau is also killing its birds after a strain of avian flu was discovered there.

Anger

Demand for chickens in both territories has dropped dramatically, with scared consumers switching to other meats or vegetables.

The birds are killed, bagged and dumped in landfill

Hong Kong consumes about 100,000 fresh chickens a day, and imports 70% of its poultry from China.

Hong Kong poultry industry retailers are angry at what they say is insufficient compensation. Jobs have been lost.

The territory's chief executive, Tung Che Hwa, wants chicken sales to resume as soon as possible.

"It was a necessary decision to protect the health of our citizens," he said. "We need to find how it happened, why it happened, very, very precisely."

Mutation fears

The infection is a new and highly virulent strain of avian flu.

In the first 24 hours, it killed almost 800 chickens, kept in cages in three separate Hong Kong markets.

A precautionary slaughter of 4,500 chickens began on Wednesday.

By Friday the disease had been discovered in 10 different places.

Local scientists say the new strain of the H5N1 virus has the potential, if left unchecked, to mutate into a virus which could cross to humans.

Most bird flu viruses do not replicate efficiently in humans.