Health authorities on Monday sealed a pharmaceutical factory due to the deaths of 31 heart patients in Lahore, suspected to be caused by a problem batch of drugs.

Earlier, the head of the investigation committee, Doctor Javed Akram said, "Since December 15, at least 23 heart patients have died in Lahore. It could be reaction of heart medicines.

"At present 110 heart patients are admitted in various hospitals of Lahore and the condition of 50 of them is critical. We have withdrawn the suspected medicines and sent samples for tests."

Akram said the committee has investigated the deaths of heart patients which occurred due to a sudden drop in white blood cells, platelets and bone marrow damage.

"The problem seems to be with just one batch of medicines provided to the Punjab Institute of Cardiology and that has been sealed," Akram said.

Health officials said a centralised data collection centre has been set up to compile information on all heart patients and a helpline had also been provided.

Lahore is the capital of Pakistan's most populous province Punjab and last year faced an outbreak of the deadly tropical disease dengue fever which killed more than 130 people.