Police said they received a report received at around noon that a construction worker had fallen from a third-floor working platform while on duty at a residential project on 15 Ki Lung Street.
The man, reportedly in his 60s, was already unconscious when officers arrived at the scene. He was rushed to Kwong Wah Hospital, and was later pronounced dead.
The Labour Department said it immediately deployed staff to the site. An investigation is now under way to determine the cause of the accident.
The death marks the second fatal workplace accident in three days — another worker died on Monday after falling from height at a construction site in Tuen Mun.
The Association for the Rights of Industrial Accident Victims said the accident in Mong Kok was the seventh industrial-related fatality this year.