The United Christian Hospital in Kwun Tong will tighten security after a small quantity of a radioactive substance was found missing from a locked room on Friday morning.
The discovery was made during a regular check, a hospital staffer said. The matter was then reported to police and the Department of Health.
Police classified the matter as theft yesterday.
The substance, Caesium-137 in jelly form, was stored in a sealed plastic bottle that was in a lead container in the hospital's nuclear medical unit, said James Chan Chi-sang, chief of service in the department of radiology and organ imaging.
Dr Chan said staff had to first get access to a room before entering another room where the substance was stored.
Both doors were equipped with electronic locks and only two radiographers had the right of access, he said.
There was no sign of burglary, he said, but maintenance work had been going on recently in the room next door.