In a tropical Chinese rainforest, seven savannah-dwelling African rhinos are said to be awaiting release into the wild -- raising fears for their welfare in a country with a booming rhino horn trade.

The animals arrived in a blaze of publicity in March at the vast Pu'er National Forest Park in the humid hills of Yunnan province in southwest China, with television images showing cranes lowering the huge beasts into paddocks.

But critics say African rhinos -- more than 150 of which have been transported to China in recent years -- will struggle to survive in the forest environment, raising doubts about the project's true purpose.

"The rhinos can't be seen by the public, you can't visit them," animal keeper Qian Fuchun told AFP in one of the park's offices.

His employer, the Mekong Group, is turning the 23,800 hectares (58,000 acres) of untouched forest in the park, home to hundreds of species of rare birds and lizards, into a tourist destination.

In South Africa, visitors to game parks are not generally allowed out of their vehicles, while they must be accompanied by an armed ranger on game walks, stay downwind of rhinos and maintain their distance.

But sketches on Qian's office walls showed visitors strolling within yards of grey rhino, shown nestled beneath trees in what was billed as a "rhino scenic zone".

AFP saw workers carving roads through the forest, where holiday homes were under construction.

"We hope the rhinos can breed here, that's our main goal... we will responsibly release them into the wild," said Qian, dressed in camouflage gear. "The project is about scientific research," he added.

The scheme comes as poaching of African white rhinos booms. The spike in killings has been blamed on high demand for rhino horn-based traditional medicine products across Southeast Asia and China, even though Beijing banned its use in 1993.

According to reports recent prices in Vietnam, the main market for rhino horn, make the powder more expensive than gold.

The white rhino is classified as "near threatened", with around 20,000 in the wild, but the South African government says poaching escalated from 13 animals in 2007 to 668 last year.

China's own Asian rhinos -- a different species -- were hunted to extinction around a century ago.

It imported more than 150 live white rhinos from South Africa from 2007-12, according to data from the Convention on International Trade in Endangered Species (CITES), which regulates the global wildlife business.

Live rhino exports to "appropriate and acceptable destinations" are permitted under CITES, but secrecy about the Chinese project has compounded concerns.

The Yunnan park's rhinos, aged between six and eight, were imported from South Africa in 2010 and kept at a city wildlife park until they were moved to the forest, the state-run China Daily newspaper said.

It quoted a keeper who said the animals "like to be tickled".

The reports "set off all kinds of alarm bells", said Tom Milliken, a rhino expert at the conservation group Traffic, adding that it was a "totally inappropriate environment" for the animals.

"These animals will just not survive in a rainforest-type environment," he said. "We have concerns about nutrition and their overall ability to cope. If they don't have supplementary food, they could starve. This is simply not conservation."

His concerns have been echoed by Chinese experts.

"This is a commercially-operated rhino husbandry project rather than an academic endeavour," Zhang Li, professor of ecology at Beijing Normal University, told local media.

The Mekong Group declined repeated requests for comment made over several weeks by AFP. Provincial authorities said the park was built "with permission" and declined further comment.

But others have drawn parallels between the project and a previous Chinese effort to import South African rhinos to a wildlife park which was exposed as a secret multimillion-dollar plan to harvest rhino horn.

More than 60 African rhinos were transported to a park in the southern province of Hainan owned by a subsidiary of a Chinese arms manufacturer, US magazine Time reported in 2011.

The park administrators' website detailed plans to "produce various rhino horn products, including 500,000 'rhino horn detox pills'", and described a device for scraping rhino horns, Time said.

South Africa has said it tightened its controls on rhino exports following Time's report. "There were no exports to China (in 2012)," a department of environment spokeswoman told a parliamentary briefing.

The introduction of rhinos to Yunnan "might be closely related to the Hainan programme", China Newsweek magazine reported last month, citing an anonymous source.

The South African restrictions are putting a squeeze on the developer's vision of expanding its herd of wild rhino, the magazine said, adding that negotiations to bring a further 30 rhinos to the park had "stalled".

But the Mekong Group's website says the company is hiring 10 keepers to care for "red pandas, rhinos... and animal breeding work".

"If you're hired, we'll treat you favourably," it says.