Two tenants of a partitioned flat in Hung Hom escaped crashing with their bunk bed five meters to the street below after the balcony they were renting collapsed at the height of the amber rainstorm signal.

One of the two, a man surnamed Chu, said he was sleeping on the lower bunk when he was awakened at around 2am yesterday by the tenant on the top bunk who felt the balcony was about to give way.

Chu said he got scared when he saw the floor "sinking" and the wall facing the street leaning outward, so he put on his trousers and started to head outside.

He then heard a loud bang and saw debris - along with their belongings - crash to the street below.

Pictures showed their bunk bed dangling from the exposed first-floor room.

The flat - which Chu said was subdivided into five rooms - was in a 60-year-old building on Gillies Avenue South.

Chu, who has been living in the building for six years, said the rent for their room was HK$3,000 a month.

According to reports, the Building Department suggested to the building's owners in 2009 that repairs be carried out because of its age. The recommendation was apparently ignored.

Police said 22 tenants were evacuated, including five Polytechnic University employees, who were given temporary shelter at the university dormitory.

The other tenants were temporarily relocated to Hung Hom Community Hall.

The area below the collapsed balcony was closed off by police and traffic in the vicinity was restricted. It is not clear when tenants would be allowed to return to the building to collect their belongings.

Ronnie Wong Kwok-ping, a Buildings Department senior surveyor, inspected the site and said the balcony's structure had been poorly maintained though he did no think the building itself would collapse.

The department had earlier checked the building and stated that two more balconies - on the second and third floors - are at risk of collapsing and in need of temporary support.

In May the department received several complaints about the building being neglected and a letter was issued urging owners to repair it.

The department said it will continue investigating the cause of the collapse.

The dean of Technological and Higher Education Institute of Hong Kong's Faculty of Science and Technology, Chua Hong, said the balcony "looked like an unauthorized building work."

He said it appeared the balcony was solely supported by concrete and steel bars attached to the building's main structure.

Chua said the steel bars could have rusted over time and could no longer support the weight of the balcony.

Police and the Fire Service Department's Urban Search And Rescue Team were sent to handle the collapse.