At least 119 people were killed in a fire which swept through a poultry processing plant in northeast China on Monday, local officials said, in what appeared to be the country's deadliest blaze for 12 years.

The fire engulfed the Baoyuan poultry plant in minutes following a blast triggered by a suspected chemical leak, according to workers quoted by various state media outlets.

More than 300 employees were in the plant at Dehui in Jilin province at the time and emergency workers were uncertain how many remained trapped inside, Xinhua news agency said.

"As of 4:25 pm, altogether 119 people died," the Jilin provincial government information office said on Sina Weibo, a service akin to Twitter.

The latest post did not say how many were injured, but the local government earlier put the number at at least 54.

It is the country's worst fire for more than a decade, according to listings on internet portal Baidu. On December 25, 2000, a blaze at a shopping centre in Luoyang, in the central province of Henan, killed 309 people.

The Southern Metropolis Daily newspaper said on its Weibo page the fire started in a workshop which had only one open door.

Fewer than 30 of up to 300 people working inside escaped the inferno, a worker told the newspaper.

"It took less than three minutes for the whole of the workshop to go up in flames," the worker said.

The slaughterhouse gate was locked when the fire broke out but about 100 workers escaped, Xinhua said. The facility had a "complicated interior structure" and narrow exits which were slowing the rescue work, it said.

The cause was not immediately clear, but state broadcaster CCTV said eyewitnesses had heard a blast and suspected a chemical leak.

CCTV also said on its Weibo account that the blaze might have started with an electric spark in the plant.

Six hours after the 6:00 am fire broke out it had largely been brought under control, CCTV said, but Xinhua added that firefighters were still working to extinguish it entirely.

CCTV showed the plant surrounded by red fire engines, with its roof apparently burnt away to reveal charred black girders.

A dramatic photo taken earlier and posted on a Hong Kong-based online news portal showed dense clouds of black smoke several times higher than the low-rise plant.

A bright blaze could be seen inside a row of windows in one part of the processing plant.

The image could not be independently verified, although the building looked similar to the one shown by CCTV.

Photos from Xinhua showed charred walls and rooftops at the plant, with a row of fire engines standing by.

The Jilin Baoyuanfeng Poultry Company, which began operations in 2009, employs 1,200 people and produces 67,000 tonnes of chicken products per year, Xinhua said.

China News Service said that as of the end of 2010 it had sales of 230 million yuan ($38 million).

Workplace safety standards can be poor in China. Fatal accidents happen regularly at mines and factories, with some blaming lax enforcement of rules.

But loss of life is rarely on such a scale as the Jilin fire.

A major blaze at a Shanghai apartment building in 2010 left 58 people dead, while a shopping mall fire in Jilin killed 53 people in 2004.

In some cases owners or company officials have been arrested as a result of workplace accidents.

No arrests were immediately reported and Xinhua said an investigation into the cause had begun.

Company representatives could not be reached for comment.