SHANGHAI — A few weeks ago, when Chinese investigators raided a small travel agency in this fast-growing city, they came upon something startling.

The agency appeared to be using fake contracts and travel invoices to help executives at the British pharmaceutical giant GlaxoSmithKline bribe doctors, hospitals, foundations and government officials, Chinese authorities said.

Soon after, the police shut Shanghai Linjiang International Travel Agency and detained its boss, Weng Jianyong. Four Chinese-born Glaxo executives were also held on suspicions of bribery and tax fraud.

But documents obtained by The New York Times show that in the last three years at least six other global pharmaceutical companies, including Merck, Novartis, Roche and Sanofi, used the same travel agency to make arrangements for events and conferences.