Three sites could be freed for homes by moving public facilities now on the land into caverns, the government proposed yesterday.
But a critic of the scheme said it would cost too much. And one site, in Sai Kung, is potentially controversial as reclamation is suggested to enlarge the area.
Details of the cavern idea, and six reclamation schemes, were announced yesterday for public consultation, a day after preliminary details were released.
Caverns, which would have to be dug into hillsides, and reclamation are among initiatives to build up a land reserve for the city, Secretary for Development Paul Chan Mo-po said.
"We need to have a reserve that goes beyond our short-term needs," he said.
Sites reclaimed or vacated by moving unpopular facilities could be used for flats, commercial, logistics, recreation and other projects, Chan said. The public will be asked if they support six reclamation schemes that could produce more than 2,000 hectares of land, and the kind of land use they would like to see.
People will also be asked for their views on the three sites identified for the cavern developments. They are in Sai Kung, Diamond Hill and Sham Tseng, and now house a sewage treatment plant, a fresh water reservoir and a salt water service reservoir.
They were chosen as pilots from 21 unpopular facilities shortlisted from 445. Compared to the 28-hectare Sha Tin Sewage Works, the three sites are tiny, ranging from 1.1 to 3 hectares and are each expected to yield a few hundred to a few thousand flats.
In Sai Kung, the sewage treatment plant at Tui Min Ho would release 2.2 hectares of land if vacated. This could be enlarged to six hectares with reclamation from the adjacent sea shore.
Wai Chi-sing, permanent secretary for development, conceded that the sites were small, adding that the government would formulate a masterplan for cavern developments with the remaining 18 sites.
Albert Lai Kwong-tak, of The Professional Commons, said it was unlikely the three projects would be cost-effective because relocating the plants and excavation work would be expensive.
An assessment for the Sha Tin project put the cost at HK$17.7 billion, which could be recouped only if luxury flats were built.
The World Green Organisation, a local group, said officials had failed to include population and housing need projections in the consultation document, making it difficult for the public to assess the scheme.