Updated at 5.12pm: A group of mainland visitors escaped injury by climbing out the windows of a blazing office in Western on Monday morning. Shortly before 2am, the ground-floor office of a decoration company on Connaught Road West burst into flames after someone threw a lit cigarette butt on the floor. Police said 14 two-way-permit holders were in the office at the time. ''Some of the mainlanders ran out the front entrance while others had to climb out of windows to escape from the burning unit,'' said a Fire Services Department spokesman. Firefighters extinguished the flames before 2.30am. The office was badly damaged but nobody was injured. Police are investigating whether the mainlander visitors were illegal labourers.