Claims of faulty piling work at a block of flats above the Airport Express' Kowloon Station have prompted officials to demand checks by the contractor.
Without revealing details of an anonymous letter sent to his office, Director of Buildings Leung Chin-man said there was sufficient evidence in the letter to merit an inquiry.
'We are taking this letter very seriously. You don't get a letter like that very often,' said Mr Leung.
He said engineers visited the construction site hours after he received the letter on Monday, but the initial check provided no evidence to support the allegation about the project, called the Waterfront.
But the contractor's foundation subcontractor, Chun Wo Building Construction, has been asked to inspect the piles for loose gravel.
Developer Hang Lung said last night it had not been contacted by the department. But all work on foundation piles had been conducted in accordance with the contracts and had been approved by on-site engineers.
The development was the biggest of 16 building plans approved by the department in January.