Chief Executive Leung Chun-ying refused to reply four times to building inspectors' queries about a suspicious wall in his Peak home after an inspection in June, it emerged yesterday.
The wall sealed a 200-square-foot room in the basement of Leung's House No 4 at Peel Rise.
A Buildings Department spokeswoman said yesterday its inspectors were aware of the wall and had asked Leung in a June 27 letter and three subsequent reminders to provide information on it.
Department staff earlier noticed that "the position of part of the external wall of the original store room did not match the original approved building plans," she said.
The spokeswoman added that, following Monday's inspection, the department asked Leung to open the wall to let its staff inspect the space inside.
Leung has insisted that he never concealed any illegal structures, explaining he had not revealed the existence of the room until last week because he had it bricked off and believed that the room no longer existed after having dealt with it.
Yesterday he said: "The authorized person representing me will follow up with the Buildings Department and study its requirements so that we can handle the illegal structures as early as possible."
The department said it will not initiate a criminal investigation hastily and will follow established procedure when determining its next actions.
Illegal structures were also found in Leung's previous residence at No 39 Tung Tau Wan Road in Stanley, including a garden canopy in 2000, with alteration works carried out later.
This was contrary to what Leung said last week, that it was the first time for him to handle illegal structures in his residence.
According to a press statement issued by the department in 2001, Leung initiated the reinstatement work at his Stanley home the year before.
However, Leung said yesterday he needed to trace back records on his former residence.
On Friday, Leung issued a 14-page statement in which he revealed for the first time that he had sealed the basement room - one of 10 illegal structures at his Peak residence - four months before the chief executive election in March. Leung also said earlier an open yard space in House No 4 was altered to a guest toilet, which the department said was unauthorized.
Meanwhile, legislators from the Civic and Democratic parties are seeking answers from Leung. Lawmaker Wu Chi-wai amended his motion of no-confidence in Executive Council member Franklin Lam Fan-keung into a motion of no-confidence in Leung, saying his integrity has been bankrupted.