A traditional Chinese medicine company at the heart of an angry Internet campaign accusing it of cruelty to animals opened one of its controversial bear bile farms to journalists on Wednesday.

Bear bile has long been used in China to treat various health problems, despite scepticism over its effectiveness and outrage over the bile extraction process, which animal rights group say is excruciatingly painful for bears.

The Guizhentang pharmaceutical company in the southeastern province of Fujian last year announced plans to raise millions of dollars through a stock exchange listing in order to increase production of the bile.

But the announcement sparked a noisy Internet campaign against the listing that brought into question the medical effectiveness of the bile and the cruel manner in which it is extracted from living bears.

According to a Guizhentang spokeswoman surnamed Wang, Chinese journalists began visiting one of the company's bear farms on Wednesday as part of attempts to address the controversy.

She said they were promised full "transparency" to inspect the premise, but the state-run Beijing News reported that journalists would not be allowed to ask questions during the visit.

"Guizhentang made public a list of journalists without prior consultations. They could be putting on a show," the paper quoted Zhang Xingsheng of the Nature Conservancy's North Asia office as saying.

The company refused to allow AFP journalists to take part in the tour, saying the event was not open to foreign reporters.

The anti-bile campaign got a boost this week after China's retired basketball superstar Yao Ming visited a sanctuary for Asiatic black bears, or moon bears, rescued from bile farms by the Animal Asia group.

"The moon bears are beautiful animals that nature has given us," the Sichuan Daily quoted Yao as saying as he toured the sanctuary. "We should all be concerned for the moon bears."

Yao has also campaigned to end the killing of sharks, harvested for their fins -- a traditional Chinese delicacy.

"It just gave me immense satisfaction that people in China are taking up this challenge of wanting bear farming to end," Jill Robinson, CEO and founder of Animals Asia told AFP.

"We have seen an unprecedented outcry from the Chinese public and media over the last few days."

Photos posted on popular web portal 163.com by reporters allowed into the farm showed a large enclosure where dozens of bears roamed around, some climbing on metallic structures, in what was called a "breeding centre".

Other photos show the black bears in small, narrow cages, and employees wearing surgical masks, hats and gloves, sticking draining tubes in the animals' gall bladders and a yellow liquid flowing into a glass.

Animals Asia, which since 1988 has been campaigning against the practice, on Tuesday published a report and video exposing what it said was the "brutal truth" behind bile extractions, in anticipation of the visit.

It said that around 7,000 bears still languish in bile farms across China, but many more could be used in illegal establishments.

Bear bile is used in China and other Asian countries to treat fevers, liver disease, eye problems and other health problems, but activists have for years tried to stop the practice, citing it as a form of torture for the bears.

Guizhentang farmed 470 bears last year, and had decided to list to increase the number to 1,200 in order to step up annual production of bile to 4,000 tonnes.