The Hong Kong Observatory raised the amber rainstorm warning signal on Sunday morning as heavy showers, exceeding 50 millimeters over Lantau Island, lashed the city.

The observatory issued the warning at 6:10 am as the heavy downpour brought about 30 mm of rainfall to many places in the territory.

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"Heavy showers this morning brought more than 30 millimeters of rainfall to most parts of the territory, and rainfall even exceeded 50 millimeters over Lantau Island and Sai Kung," the observatory said.

A thunderstorm warning issued at 5:05 am was also extended until 1 pm, the HKO said, urging members of the public to take precautions. It added that there will be flooding in some low-lying and poorly drained areas.

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A broad trough of low pressure and an active southerly airstream was bringing thundery showers to the coast of Guangdong and the northern part of the South China Sea, the observatory said.

The HKO added that the weather in Hong Kong on Sunday was forecast to be cloudy with showers and squally thunderstorms, with the maximum temperature at around 28 degrees Celsius. More showers and thunderstorms were expected on Monday morning.