The Hong Kong tropical cyclone warning signals, or informally typhoon signals, are a set of signals used to indicate the threat or effects of a tropical cyclone. The Hong Kong Observatory issues the warning signal if a tropical cyclone approaches within 800 kilometres (432 nmi; 497 mi) of Hong Kong and poses a threat of deteriorating conditions in Hong Kong. The signals are represented as a set of numbers and symbols. Previously lights were also used at night.