I called Town Council last Saturday and they sent someone down in 2 hours. After checking he said it was ceiling leak so must call HDB. He said TC will update the system and HDB will call me on Monday.They did call and we have made arrangement for viewing this Thursday (yeah, HDB schedule is tight).
Just to add, the TC guy mentions that vertical pipes (those coming out of ceiling) belongs to Town Councils. Horizontal pipes are owner's responsibility. Ceiling is HDB.