The government has been urged to introduce legislation to better protect people working outside in the sweltering heat.

Greenpeace and the Hong Kong Catholic Commission for Labour Affairs made the appeal on Wednesday.

They said they had carried out a survey involving 150 outdoor workers from August to September, with more than half reporting they had experienced symptoms of illness caused by heat in the past two months, such as dizziness and difficulty in breathing.

The two organisations said many employers fail to put in place preventative measures, such as providing outdoor workers with handheld fans or sun hats.

Ping, a 63-year-old pest control worker, said she once felt dizzy working under the sun on Lamma, adding that having to wear protective gear in the sweltering heat makes her job much harder.

“Your entire body is drenched in sweat while wearing the protective suit...your goggles and gas mask are all wet," she said.

"Water is provided but sometimes in bottles that are too small, so it's not enough."

Law Pui-shan, policy research officer at the Hong Kong Catholic Commission for Labour Affairs, said legislation is needed to hold employers accountable.

She said there are only guidelines on preventing heatstroke at work and the Occupational Safety and Health Ordinance doesn't set out concrete safety standards regarding heat-related illnesses.

"The guidelines are not legally binding, nor can they be used as a standard for conviction...It's not enough to make employers comply with the relevant requirements set out in the guidelines on preventing heatstroke at work," she said.

Law also urged the administration to consider heatstroke and other heat-related illnesses as compensable occupational diseases.

Labour Secretary Chris Sun recently said the government plans to use the observatory's heat index to formulate more comprehensive guidelines to prevent workers from getting heatstroke.

Greenpeace campaigner Tom Ng said it is good that authorities want to use the index as a reference point.

"This is a good step, but when it only goes into the guideline, it's not actually making sure that the employees get whatever the benefits this index would bring, so it should go into a regulation. The regulation should make good use of this heat index to say [when] employees get to a certain level of risk, they should get help," he said.