Hong Kong Observatory has issued the amber rainstorm warning signal at 12.10pm, indicating rainfall exceeding 30millimeter per hour.
It urged residents who are likely to be affected to take necessary precautions to avoid possible flood damage as heavy rain may bring about flash floods.
Heavy showers and squally thunderstorms have been predicted in the afternoon in Hong Kong.
There will be fewer showers later tonight, the Hong Kong Observatory said.
The intense thundery showers are associated with an upper-air disturbance affecting the vicinity of the Pearl River Estuary, along with the area of low pressure over the central part of the Philippines, bringing unsettled weather to the region.