Four American Christians are staging a sit-in at a Chinese airport, which they refuse to leave until the authorities return 315 Bibles they were trying to bring into the country.

The group - from Vision Beyond Borders - spent the night sleeping on couches at Kunming airport in southern Yunnan Province after customs officials removed the Chinese language bibles from their luggage.

The bibles were printed in Indonesia, transferred to Thailand and transported to Kunming in duffel bags by the Wyoming-based group which distributes bibles around the world.

Pat Klein, one of the members of the group, told reporters that he was bringing the books into China because his contacts in the Chinese Christian community were unable to get hold of sufficient copies.

Bibles are widely available in Chinese bookstores, though only versions and translations authorised by the authorities.

Although a nominally atheist country, China is home to a rapidly growing number of Christians. A single domestic publisher - approved by the government-backed Christian association - claims to produce 8.000,000 copies per month.

This makes it the largest Bible-publishing factory in the world, but the copies are printed under supervision for use at authorised churches and hotels. Customs officers restrict imports of Bibles and other material deemed "harmful" to stability.

"I heard that there's freedom of religion in China, so why is there a problem for us to bring Bibles?" Klein told the Associated Press.

The customs office in Kunming said it was "dealing with the issue", but declined to comment further.

Religious in China has come under scrutiny since the start of the Olympics, partly because US president George Bush used his visit for the opening ceremony in Beijing to visit a church and to call for people to worship freely.

According to a human rights group, a Chinese Christian activist - Hua Huiqi - was detained by police and then escaped on his way to the same service. Police deny detaining Hua.