It is also the second time in less than a week in which police have been asked to investigate.

The latest scare involves 17,000 tablets of the diabetic drug metformin which have been dispensed mainly to patients on the west side of Hong Kong Island.

Authority chairman Anthony Wu Ting-yuk said the investigation involves the 500-tablet package produced by Christo Pharmaceuticals.

"We are handing the matter to the police, for them to investigate whether any wrongdoing has occurred. We believe there may have been deceit involved," Wu said. "If a company has lied and we find out, consequences will be severe."

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Wu said more than 300 patients are currently using metformin, including those at Queen Mary Hospital and in the Sai Ying Pun and Aberdeen districts.

"The Department of Health says that the safety and quality of the drugs are satisfactory," Wu said.

"But we will accommodate patients who want to return their drugs."

Chief of pharmacy service, Hong Kong West Cluster, William Chui Chun- ming said hospitals have started contacting affected patients to explain what has occurred and give them the option to exchange their medication.

He added the authority will review current mechanisms to strengthen supervision and avoid overdependence on a single supplier.

A department spokesman confirmed it acted following media inquiries about the two sizes of metformin packages that were identically labeled HK-47363.

The department found that one of them was not registered.

It said 25,000 of the 38,000 metformin tablets supplied to the authority were unregistered. These were in 500-tablet packages.

The remaining 13,000, in 100-tablet packages, were registered.

The sale of unregistered pharmaceutical products is an offense under the Pharmacy and Poisons Ordinance and carries a maximum penalty of two years' imprisonment and a HK$100,000 fine.

Earlier this month, executives at Marching Pharmaceutical were arrested after it was found they had issued a recall notice for certain products without the approval of the department.

In addition, operations at pharmaceutical firm Europharm were suspended after six deaths were linked to one of its gout-treatment drugs, which allegedly contained 10 times the normal level of a common fungus.