Hong Kong police and the Department of Health last night were investigating the theft of a small quantity of a radioactive substance from a Kowloon public hospital.
The Hospital Authority said the substance, Caesium-137, was found missing yesterday morning during a regular check by a member of staff of United Christian Hospital in Kwun Tong.
Under the licensing system, radioactive substances should be properly sealed and stored inside a locked venue. However, an authority spokesman said last night that recent maintenance work at the hospital may have left the substance vulnerable to interference.
The caesium-137 is stored in the nuclear medicine unit of the hospital.
In a statement issued last night by the Department of Health, a departmental expert said the level of radioactivity of the missing substance was low.
According to the United States' Centres for Disease Control and Prevention, exposure to caesium-137 can generate high-energy gamma radiation which can increase the risk of the person exposed to it of getting cancer.
But the authority spokesman said someone exposed to the substance at close quarters for a long period of time could receive a level of exposure similar to that delivered during an X-ray. Exposure at a distance of more than a metre was harmless.
The hospital reported the theft to police.
The force's Ngau Tau Kok division is investigating the case.
The authority urged anyone who knew the whereabouts of the caesium-137 to inform the police.
Caesium-137 is used in small amounts for calibration of radiation-detection equipment. It is used in larger quantities in radiation therapy devices for treating cancers.
If an intruder stole the caesium-137, it would be the second recent case in which someone has gone into a hospital and committed a crime.
A man was jailed for two months for stealing three test tubes of blood at Yan Chai Hospital in September and swallowing the contents.