The concern arose after there were 15 reports of windows crashing to the pavement this month, including several cases recently.

Speaking at a press conference on Monday, Buildings Department chief structural engineer Leung Siu-man said its engineers were still trying to find out the reason.

He said there were only 40 cases of windows falling last year.

Leung said the problem of aluminum windows is not major but these minor problems could have serious consequences if people continue to ignore the problems and refuse to hire trained technicians to check and repair them.

According to Leung there are tens of millions of aluminum windows in Hong Kong, many of them installed more than 20 years ago. He urged people to have their windows checked at least once a year.

Engineers said aluminum windows easily become detached and fall to the street if they are not checked, particularly after stormy weather.

Windows with rusted joints could fail when opened with excessive force.

On Monday morning, a piece of glazed aluminum window frame became detached from an apartment on the 25th floor of Block C of On Ning Garden in Tseung Kwan O.

Police arrested a 41-year-old woman who was cleaning it. No one was injured. The woman was released on HK$100 bail.

Monday's incident came just a day after a similar window failure in the same premises.

The Owners' Incorporation said some residents hung clothes from their windows claiming this may be a danger to the public.

On June 22, an aluminum window fell from the 12th floor of Cheung Wong Mansion in Mong Kok. It hit a 24-year-old Indonesian maid, injuring her.

The window is part of a public corridor on the 12th floor of the 30-year-old residential building.

The maid was taken to Kwong Wah Hospital and discharged on June 26.

Elsewhere on Monday, a window fell to the podium of Billion Court in Ap Lei Chau just as a resident on the 17th floor opened it.

Meanwhile in North Point, a security guard reported a window missing from the 12th floor of the Wiseman Building.

In the afternoon, police received reports of a fallen piece of window which had become detached from the 22nd floor of Iuki Tower in Wan Chai and damaged two vans at the junction of O'Brien Road and Thomson Road.

Last Saturday, a window frame fell from a residential block in Mei Foo Sun Chuen, Cheung Sha Wan as a 44-year-old woman was opening the window in her kitchen.

And on Sunday, a window became detached from Hsin Kuang Centre Block 1, Wong Tai Sin when a 68-year-old man was cleaning it.

dennis.ng@singtaonewscorp.com