The Asian financial hub of Hong Kong was drenched on Friday by the heaviest rain since records began 140 years ago, killing one person and injuring 83 others.

Videos showed cascades of water surging down steep hillsides in the former British colony, flooding waist-deep in narrow streets, and inundating malls, metro stations and tunnels.

Experts said Climate change increased the intensity of tropical storms, with more rain and stronger gusts leading to flash floods and coastal damage.

The heavy rainfall in Hong Kong started on Thursday and in the hour leading up to midnight, the city's weather observatory recorded hourly rainfall of 158.1 millimetres at its headquarters, the highest since records began in 1884.

Authorities therefore issued flash flood warnings, with emergency services conducting rescue operations in parts of the territory.

The observatory also warned residents living in close proximity to rivers to pay attention to weather conditions and consider evacuation if their homes are flooded, stressing that there were potential landslips, telling motorists to keep away from steep slopes or retaining walls.

Meanwhile, Hong Kong's stock exchange cancelled all trading sessions on Friday.

At a press conference, Hong Kong Chief Secretary Eric Chan described the deluge as "a once-in-a-century heavy rainstorm", adding that extreme conditions would continue until midnight local time (1600 GMT).

"It's like putting four bathtubs of water into one bathtub... it will spill," Chan said, when asked if the government had done enough to prevent flooding.