Record-breaking rainfall paralyzed much of Hong Kong on Friday, with flash flooding submerging metro stations and trapping drivers on roads, as authorities suspended schools and urged the public to seek safe shelter.

Photos and videos showed residents wading through murky brown floodwaters as heavy rains continued to fall. In some low lying areas, streets were transformed into surging torrents, with authorities forced to rescue motorists stuck in their vehicles.

The deluge began late Thursday night, with the Hong Kong Observatory recording more than 158 millimeters (6.2 inches) in rain between 11 p.m. and midnight, the highest hourly rainfall since records began in 1884, the government said in a news release.

Some parts of the densely populated city of 7.5 million saw almost 500 mm (19.7 inches) of rainfall in 24 hours, according to online weather data site OGimet.

The extreme conditions caught many residents by surprise and come just days after Hong Kong was lashed by its strongest typhoon in five years.

Typhoon Saola, originally a super typhoon, weakened to the equivalent of a Category 2 hurricane as it reached Hong Kong – but was still potent enough to knock down trees and cause hundreds of flight cancellations. Eighty-six people were injured from the typhoon, the government said.

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Friday’s deluge caused widespread transport and business disruptions across the financial hub, with the stock market canceling morning trading, and all schools closed for the day. On Friday, authorities appealed to businesses to allow non-essential employees to stay at home or seek safe shelter, citing unsafe travel conditions.

The city’s Mass Transit Railway announced it would suspend services on one of its lines after a station in the Wong Tai Sin district was flooded, with footage shared widely online showing floodwater gushing down the stairs.

While most other subway operations remained open, all major bus, tram and ferry services were suspended, according to public broadcaster RTHK. Multiple roads have also been closed off due to the threat of landslides.

The city remains under its highest “black” rainstorm warning, issued Thursday evening. At the time, the official weather bureau urged people to stay indoors and find shelter, and for residents near rivers to consider evacuating.

A bus drives through a flooded area in Hong Kong on September 8, 2023. Tyrone Siu/Reuters

The government also warned “there may be a risk of flooding” in its northern New Territories district, which is adjacent to the Chinese mainland, after the neighbouring city of Shenzhen said it would release water from a reservoir.