China National Radio said the city of Zhengzhou has taken steps to "hold 18 GlaxoSmithKline employees and medical personnel," The Wall Street Journal reported Saturday.
Authorities did not respond to request for comments, the Journal said.
China has previously said it was investigating the company for allegedly bribing doctors with kickbacks and sexual favors to get them to prescribe their products and raise prices of drugs.
It was already known that China had detained four GlaxoSmithKline executives.
Chinese authorities said Friday a fifth executive, Mark Reilly -- the company's former general manager for China -- would return to China to assist in the investigation.
China's officials Xinhua News Agency had reported several company employees have confessed to bribery, The New York Times said.