The observatory said the temperature at its headquarters in Tsim Sha Tsui reached 35.9 degrees Celsius on Tuesday afternoon, making it the hottest day on record for September.

Some districts recorded even higher temperatures, including Sheung Shui at 38.2 degrees Celsius, and 37.2 degrees Celsius at Sham Shui Po and Wong Tai Sin.

Leung Wing-mo from the Hong Kong Meteorological Society attributed the sweltering heat to Typhoon Muifa, which is expected to make landfall in eastern China.

"We are being affected by the subsiding air of Typhoon Muifa, and any subsiding air is a warm one, which is hotter than it normally should be. The wind strength in Hong Kong today is rather weak, which is not conducive to dispersing the hot air," Leung told RTHK, adding that the intense heat will likely affect the city for a few more days.

Hong Kong also recorded high air pollution levels since last week, with some districts reaching the "serious" category on Tuesday.

The Environmental Protection Department said it expects air pollution levels to remain high over the next few days, and advised outdoor workers to take appropriate preventive measures.