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.

Hong Kong's weather bureau said its highest "black" rainstorm warning would remain in place until 11am on Tuesday (Aug 5), as heavy rains lashed the Asian financial hub, closing hospital wards, schools and the jurisdiction's courts and register offices.

Forecaster issued highest-level storm warning at 5.50am, prompting authorities to suspend all morning and whole-day schools.