An elderly man was in critical condition after being struck by lightning in Hong Kong on Tuesday evening shortly before an amber rainstorm warning was issued.

The Hong Kong Observatory had warned of serious flooding in parts of Hong Kong Island, saying more than 70mm of hourly rainfall had fallen or was expected in Southern district, and residents should take necessary precautions.

From 7pm to 8pm, most of Hong Kong Island experienced 30mm to 40mm of rain, with areas including Tai Tam and Aberdeen seeing more than 40mm. Parts of Lamma Island were also hit by 30mm to 40mm of rain.

On Lamma Island, a 77-year-old expatriate man was hit by lightning at a coastal spot at Sok Kwu Wan at about 7.20pm. The Briton, who suffered shoulder and chest injuries, had been on a speedboat with his wife. He was taken to Aberdeen marine police base before being transferred to Queen Mary Hospital in Pok Fu Lam.

The amber alert was issued at 7.35pm, meaning heavy rain had fallen or was expected to fall generally over Hong Kong, exceeding 30mm in an hour and was likely to continue. The warning signal was cancelled at 8.45pm.

Meanwhile, a thunderstorm warning was issued at 5.55pm and remained in force until 10pm. Intense gusts of around 70km/h were recorded at outlying island Cheung Chau at about 7.40pm.

It was the second amber warning issued on Tuesday, with the first at 3.45am and which remained in force until 6.40am. As of 7am, more than 30mm of rainfall was recorded over most of the city, with Tai Po and North district seeing over 50mm.

Drivers should also beware there was likely to be serious road flooding and traffic congestion.

An active trough of low pressure was bringing thundery showers to the coast of Guangdong including Hong Kong. Showers will be heavy at times, with moderate to fresh south to southwesterly winds.

Heavy showers and squally thunderstorms are also expected in the following couple of days.