At least 112 people were killed in a fire at a poultry processing plant in northeastern China on Monday, local officials said, in what appeared to be the country's worst blaze for 12 years.

More than 300 workers were at the Baoyuan poultry plant at Dehui in Jilin province when the fire broke out and emergency workers searching for survivors were uncertain how many remained trapped inside, Xinhua news agency said.

"As of 3:20 pm, altogether 112 people had died," the Jilin provincial government information office said on its Weibo account, a service akin to Twitter.

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

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

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

The cause of the blaze was not immediately clear, but state broadcaster CCTV said eyewitnesses had heard a blast and suspected a leak of liquid ammonia.

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

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

A dramatic photo taken earlier in the day from an unnamed Weibo account and posted on a Hong Kong-based online news portal showed dense clouds of black smoke several times higher than the low-slung 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, where 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, and one at a shopping mall in Jilin killed 53 people in 2004.

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

It was not clear whether poor standards were to blame for the blaze in Dehui.

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

Company representatives could not be reached for comment. (AP)