A bicycle caught fire at about 11pm on 20 October in a car-park podium garden at Kwai Fong Estate. Security guards put it out.
Footage described by HK01 showed one guard beating at the flames with a broom while two colleagues used water. A resident quoted by the outlet said the fire was under control within three minutes.
Police found a 14-year-old nearby with burns to his face and arm and arrested him on suspicion of arson. He was taken by ambulance to hospital. Police said their preliminary belief was that someone used a gas canister and lighter to set the bicycle alight, and that the flame flared back and burned him.
Police arrested a second 14-year-old on suspicion of arson the following day. Both teenagers were being held for investigation.