Planning Department chief Ava Ng Tse Suk-ying defended the policy Monday, arguing that the air ventilation factor has been taken into consideration with regard to the auction of all prime sites on the land application list.

She said the erection of tall buildings at these sites will not create any "wall effect."

"For all the sites to be incorporated in the land application list, we have done all sorts of detailed assessments, including air ventilation assessment research," Ng said.

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Environmental group Green Sense had earlier demanded the withdrawal of prime sites in West Kowloon from the land application list, warning that skyscrapers slated to be built there would pose a serious threat to the health of residents, especially the elderly, because of the "wall effect."

The group identified at least 12 plots in the densely populated districts of Yau Ma Tei, Hung Hom, Wong Tai Sin and Tung Chung as likely to be packed with high-rises on the waterfront, notably the Hoi Wan Road site.

But Ng noted that no air ventilation assessment has been made for the Hoi Wan Road site as the area covers only about 8,000 square meters, which is not big enough for such a requirement.

Under the technical guidelines jointly issued by the Environment, Transport and Works Bureau and the Housing, Planning and Lands Bureau last year, an air ventilation assessment is required only for sites with a total gross floor area of more than 100,000 square meters.