A concern group on Wednesday urged the Labour Department to beef up its guidelines on working under hot weather.

The department issued the "Guidance Notes on Prevention of Heat Stroke at Work” more than a year ago, outlining the criteria for outdoor workers to take hourly breaks during extreme conditions to prevent heatstroke.

An updated version was issued earlier this year, aligning the department’s warning system to the Hong Kong Observatory's "extremely hot special weather tips".

But the document also states that employers or contractors could abolish breaks for workers if certain measures are implemented to prevent heatstroke, such as providing drinking water, cooling vests and portable fans.

The Concern for Grassroots' Livelihood Alliance said 90 percent of 100 cleaners responding to their recent survey said they felt unwell even when preventive measures were in place.

According to social worker Au Yee-wing from the alliance, many cleaners said the guidelines failed to address their needs.

She said, for example, that employees working in extreme hot weather wearing protective suits are granted extra rest time, but those wearing only masks are not.

"Street cleaners wear masks while working in the hot environment. We suggest the Labour Department review the guidelines, allowing cleaners to increase their rest time," she said.

Au added that cleaners often have heavy workloads, making it even more difficult for them to take breaks.