Chinese airport security have seized over 300 “illegal” Bibles from four visiting American Christians on Sunday, saying it's illegal to bring the books into the country.

US missionary Pat Klein, who runs a group called Vision Beyond Borders says customs officials confiscated the Chinese-language Bibles after the group flew into Kunming from Thailand yesterday.

The officials were not immediately available for comment and a police official in Kunming said he was not able to confirm the seizure.

Klein, a 46-year-old from Wyoming says he's brought more than 10,000 Bibles into China in the past 20 years, but has never had books seized before.