Authorities issued the amber heat stress warning for outdoor workers on Thursday, the lowest of the three-level system.

According to the Observatory, an anticyclone has made it very hot over the coast of Guangdong, as local temperatures over many places rose to 33 degrees Celsius or above around noon.

At around 2pm, the mercury at weather stations in Kowloon City and Cheung Chau even reached 35 and 36 degrees, respectively.

The warning was withdrawn at 4.30 pm after being in force for a few hours.

The Labour Department said as the heat stress warning is in effect, employers should take measures to lower heat stroke risks for workers, such as giving water breaks and re-scheduling work periods.

It expressed sorrow over the death of a 42-year-old worker on Wednesday after fainting in a construction site at the Prince of Wales Hospital.

Deputy labour commissioner Vincent Ho said an initial probe showed the worker's employers had taken heat stress preventive measures and that he had been going about his duties in a shaded area.

Regardless of the fact that no heat stress warning was issued on Wednesday, Ho stressed that the safety of workers should always come first.

"With or without a heat stress warning, our guidelines state that all workers should take a break after working for a certain period," he said.

"Even when it's cooler during the autumn, workers should have a 10 to 15 minute break after two hours of work.

"If it's hot, then everyone should be even more cautious."

Meanwhile, the department and the Occupational Safety and Health Council are sponsoring firms and unions to buy products such as cooling vests and fans at discounted prices.