Last updated at 7.23pm: About 200 staff and visitors escaped unhurt when a fire broke out on the roof of Melbourne Plaza in the heart of Central's business and shopping district on Wednesday.
Black smoke blanketed the sky above the 24-storey commercial building as workers were returning to the building after lunch.
A security guard called in the emergency at 2.20pm and gave evacuation orders as no fire alarm had gone off.
''I didn't know a fire had broken out until a doctor next door told me to escape,'' Roy Ng Lo-ngai, a travel agent working on the 11th floor told SCMP.com.
''There was another small fire just two months ago, no alarms went off then. And there was yet another blaze about three years ago. I feel unsafe working here,'' he added.
Four workers were doing welding work when some sparks hit one of the two four-metre tall glass fibre water tanks setting it alight, Central District Senior Station Officer Chung Man-biu said.