The rareness of this super-sized property had made it immune to the economic downturn and the turmoil from the terrorist attacks in the United States, said Koh Keng-shing, managing director of Landscope Surveyors, the property's sole agent.

He said potential buyers of the property would be the 'super-rich', whose financial position remained intact from the downturn, while the sale would be a rare opportunity for them.

With an asking price of HK$43.8 million, the property could easily fetch HK$50 million to HK$60 million in a boom market, he said.

Mr Koh said few purpose-built apartments in Hong Kong were so large. Even townhouses rarely would exceed 4,000 sq ft in size.

A check of properties by Landscope revealed that Tregunter Towers One and Two had four such king-sized apartments as duplex units while Tower Three had one, which is retained by the building's developer, Allied Properties, as a private club.

The Albany in Mid-Levels, majority owned by Swire Properties, has one 6,400 sq ft unit and another of 7,000 sq ft.

Aigburth, in Mid-Levels - also developed by Kerry - has one 8,550 sq ft penthouse and four 6,512 sq ft units, all occupying the whole floor.

Mr Koh said most of these properties would not be released for sale as they were either leased or for owners' private use.

Apart from these properties, Mr Koh said supply of king-sized properties could come from other projects, although the quantity would be small.

There was speculation that Henderson Land Development would retain one super-sized unit at Regence Royale in Mid-Levels for its director's residence, but this had not been finalised and construction of the property was not complete, he said.

Central Development and Amoy Properties' two new residential buildings at Stubbs Road, Mid-Levels east, probably would offer some king-sized apartments, but details were not available as the projects had not been completed, said Mr Koh.

He believed these two developments would have only one king-sized apartment because rental apartments usually were smaller.

Mr Koh said combined units might be very large, but their design would be inferior to purpose-built, king-sized apartments and alteration works might be needed.

For instance, combined units might have duplicate kitchens and toilets.

He said Kerry's duplex unit at Tregunter Tower Two had four en-suite bedrooms, suitable for residence by four couples.

Mr Koh said this design was particularly attractive to Indian families who often preferred to have members of several generations living together.

He added that apartments would offer better security to property owners than would be available in houses, as well as fewer maintenance problems.