The Hong Kong Observatory issued an amber rainstorm warning at 6.15pm on Tuesday, signalling that more than 30mm (1.2 inches) of rain had fallen or was expected to fall across the city within an hour.
The forecaster said downpours were likely to continue, with unsettled weather expected over the next few days.
“Heavy showers and squally thunderstorms associated with the southwest monsoon and a trough of low pressure are affecting the coast of Guangdong and the northern part of the South China Sea persistently,” it said.
It added that the trough would continue to influence the region in the coming days, bringing further heavy showers and thunderstorms.
But with the subtropical ridge over the western North Pacific forecast to extend westwards later in the week, showers over Guangdong were expected to ease gradually.