Health authorities in the southern Chinese coastal city of Xiamen plan to probe an assisted reproduction clinic after local media exposed a secretive surrogacy service that’s reportedly helping deliver more than 300 babies a year.

Undercover reporters at Shanghai-based The Paper visited clinics in Hangzhou and Xiamen controlled by Longduhua Medical Group (Hong Kong), which provides surrogacy, a practice that’s illegal under Chinese law.

The Paper contacted the local branches of China’s top health regulator — the National Health Commission — before running the video and story Monday. Health authorities in Hangzhou and Xiamen vowed to investigate.