A Hong Kong medical center has suspended operations and its staff are being investigated after allegations it administered unregulated HPV vaccines, mostly to women from the Chinese mainland seeking easier and safer access to the shots.

AMH Medical Diagnostic Group was reportedly offering injections of the Gardasil 9 vaccine, which prevents some types of human papillomavirus (HPV), a common sexually transmitted disease which can cause cervical cancer.

The company said its bank accounts had been frozen and its staff were in legal strife after several Hong Kong media outlets reported the allegations.

U.S.-based Merck Sharp & Dohme, which makes the vaccines, said in a statement in May that AMH had not acquired them from authorized dealers. Reports alleged the company had smuggled the product into Hong Kong.

The vaccine itself has been proven safe and effective in preventing cases of HPV, but smuggled vaccines are sometimes stored at the wrong temperature which can render them ineffective. It is also hard to guarantee they are genuine.

AMH is not alone in facing smuggling allegations. The Hong Kong government said it suspects about 20 medical centers have engaged in similar activities. An investigation is ongoing.

The reports follow multiple scandals on the mainland involving substandard vaccines.

Related: Dozens Injected With Unauthorized HPV Vaccines at Hainan Hospital

Contact reporter Zhao Runhua (runhuazhao@caixin.com)