SEOUL (Reuters) - South Korea has ordered its biggest-ever cull of chickens and other poultry, gassing millions of birds to fight an avian flu outbreak spreading at what the government called an unprecedented rate.

Most of the birds culled were egg-laying hens, sending local egg prices sharply higher. Among the first consumers to react, bakeries said they were are cutting down on egg purchases and some families said they were switching to other foods.

The Agriculture Ministry said on Friday it had ordered the cull of 4 million more birds, which would take to 16 million the total number killed since mid-November, or almost one-fifth of the poultry population.

On Thursday, South Korea raised its bird flu alert status to the highest level for the first time, because of the rapid spread of the H5N6 virus.

The government has said it has found 54 cases of the virus in poultry since the first outbreak was reported on Nov. 18.

“It appears to be more highly pathogenic and it is spreading more quickly than the H5N8 virus that occurred in 2014,” Agriculture Minister Kim Jae-soo told reporters.

About 14 million birds were culled until that outbreak was finally brought under control in November 2015.

South Korean health officials bury chickens at a poultry farm where the highly pathogenic H5N6 bird flu virus broke out in Haenam, South Korea, November 17, 2016. Yonhap/via REUTERS

“We have appointed a central emergency measures headquarters to oversee the situation and reinforce our pan-governmental response measures,” added Kim.

He was flanked by officials who, like him, were wearing the yellow windbreakers donned during emergencies.

Although cases of human infections from the H5N6 virus have been previously reported elsewhere, including China, no cases of human infections have ever been detected in South Korea.

Outbreaks of avian influenza have been reported recently in Japan and several European nations, including France, which widened “high risk” restrictions nationwide last week.

Authorities in the southern Chinese city of Macau temporarily closed a poultry market and halted sales of live birds citywide after a trader tested positive for its first human case of the H7N9 bird flu virus, the government said.

The 58-year-old man has been quarantined in hospital and has yet to show symptoms. More than 10,000 chickens and pigeons at the Nam Yue market were culled on Tuesday after the discovery of the virus.

In Seoul, the average retail price for 30 eggs had risen 15 percent to 6,279 won ($5.31) by Thursday since the outbreak began, the state-run Korea Agro-Fisheries & Food Trade Corp said, adding that prices were likely to rise further.

“(Eggs) are too expensive...I make rolled omelet often for my meals, but I guess I would have to change it to things like fishcake. My family consumes around two trays per month, but because of the price I would have to make it one,” said 67-year-old Jun Chang-gil, who was shopping at Lotte Mart in Seoul.

Sim Jae-hak, a baker at the Humming Bella cafe in Seoul, said its menu was being changed to include more mousse and cheese cake, items that use fewer eggs.

The agriculture ministry said it would consider a temporary shutdown of slaughterhouses and animal feed factories if necessary to limit the spread of the virus.

The ministry had already stepped up quarantine measures, including a temporary nationwide ban on poultry transport.