The department said there was no indication the pills were unsafe.

Four hours after the department revealed the problem - which involves amitriptyline pills sold by Unipharm Trading - Secretary for Food and Health York Chow Yat-ngok announced the setting up of a high-level committee to review drug safety and industry conduct.

Dr Chow said he was 'extremely concerned' about the repeated incidents involving drug supplies.

The latest incident - the first related to imported drugs - was the fourth case in less than two weeks.

Fungal contamination in anti-gout drugs made by a Tai Po firm has been linked to six deaths; drugs produced by another local company carried the wrong expiry dates; and a third company was found to have sold unregistered diabetes medicine to public hospitals.

Deputy Director of Health Gloria Tam Lai-fun disclosed the problem with Unipharm. She said the company, which has no licence to make or package drugs, had illegally packaged for sale more than 2 million amitriptyline tablets made in Britain.

Department of Health staff raided Unipharm's premises in Kwai Chung on Tuesday. The company confessed to illegal packaging.

Police arrested two Unipharm employees the same day.

The products involved are bottles of 25mg tablets carrying batch numbers AB725 and AB755 and bottles of 10mg tablets carrying batch number AA573. Each bottle holds 500 tablets.

The department ordered Unipharm to recall the pills from shops and told doctors and pharmacists to stop dispensing them to patients.

Amitriptyline pills already dispensed will not be recalled. Dr Tam said patients should ask their doctors whether they should stop using the pills.

'We have not ordered a mandatory recall ... The hygiene of the packaging premises is acceptable. There is no safety issue involved,' Dr Tam said.

The department is also investigating whether cosalgesic, a painkiller Unipharm imported from Britain, carries fabricated expiry dates.

Unipharm refused to comment.

The Hospital Authority said it had stopped dispensing the amitriptyline pills but would not issue replacements for those already dispensed.

William Chui Chun-ming, education director of the Society of Hospital Pharmacists, said the department's supervision of the industry had 'totally collapsed'.

He criticised the decision not to recall the amitriptyline pills. He said the drug's efficacy could be affected by humidity and the temperature during the packaging process. Patients suffering depression could become suicidal if the the drug was not strong enough, he said.

Former president of the Hong Kong Medical Association Choi Kin also questioned the department's 'inaction' against Unipharm.

'The company has confessed to illegal packaging but the department endorsed it and does nothing about it. The department is obviously incompetent,' Dr Choi said.