A green group has asked the government to consider whether it is advisable to propose high-rise development in the Tung Chung river valley, which has marble caverns beneath it and is susceptible to landslides.
Green Power has written to the Civil Engineering and Development Department expressing 'serious concerns' as the government launches a consultancy study on options for extending Tung Chung new town.
The group is also worried about any development that might affect the ecologically sensitive river mouth and nearby coast.
'For the sake of public safety, the government would normally avoid allocating residential development in areas vulnerable to landslide,' the group's head of scientific research and conservation, Dr Cheng Luk-ki, said, citing the southeastern slope of Castle Peak, where no development has been allowed since a big landslide in 1990.
But he fears that officials will not heed the advice this time.
'I am worried that the government may swing to the extreme, under the banner of boosting housing and land supply,' he said.
Cheng said there were destructive landslides on Nei Lak Shan beside the valley in 1995 and 2008 and a recurrence could not be ruled out.
A geological survey by the Geotechnical Engineering Office and literature from the department confirmed the existence of marble strata beneath Tung Chung, as in the case of Yuen Long and Ma On Shan, where cavities caused problems in housing constructions.
The government wants to expand the population of Tung Chung from its present 78,400 to 220,000, with most of the extension lying to the west of existing development, and 'will carry out detailed technical studies to assess the impacts, including slope safety and cavern,' a department spokesman said.
He said the consultant would gather public views on the development options until August 12.