Blackened skies unleashed torrential rains on Hong Kong and the high-tech cities surrounding south China's Pearl River Delta on Tuesday, shutting hospitals, schools and law courts, and turning the Asian financial centre's many staircases into waterfalls.

Hong Kong came to a standstill on Tuesday as torrential rain pounded the city for the second time in less than six hours, triggering a rare black rainstorm warning, paralysing public services and flooding key urban districts.

Record-setting rain has brought chaos to parts of Hong Kong, with submerged streets, stranded buses and landslides. Residents were advised to avoid going out.