Spain will suffer its first heatwave of the summer starting on Thursday, the meteorology service AEMET said, as the government kicked off on Wednesday a heat risk awareness campaign for people working mostly outside.

After the Iberian Peninsula saw cooler than usual weather so far this summer, AEMET expects temperatures to exceed 38 degrees Celsius in most of the country on Thursday, reaching as much as 42-44 C in the southern Guadalquivir Valley. The peak of this episode will be on Friday, when most areas will warm up to 40 C.

AEMET has issued a heatwave warning for a large part of Spain, including the Balearic islands in the Mediterranean.

The National Institute for Safety and Health at Work launched the campaign "With sun it's time for caution" on Wednesday to address the risks such as heat stroke and solar radiation.

AEMET's orange-level severe heat alert in parts of the country will also trigger a ban on some outdoor working in the afternoon under a government decree approved last year to cope with more and more frequent heatwaves as a result of fossil fuel-driven climate change.

The measure affects outdoors working such as street cleaning and agriculture.

"There are people who are highly affected by such high temperatures, by exposure over many hours and no proper hydration... so my main advice is don’t underestimate them because the body is not prepared to withstand those conditions too long," AEMET spokesperson Luis Banon told Reuters.

The heatwave is expected to last until Saturday although heat could persist until the middle of next week and will be accompanied by haze coming from Africa, which often exacerbates health problems during heat episodes.

In Madrid, where thermometers registered 36 C on Wednesday, people tried to cool off at parks and fountains.

"I cope by using a fan if I'm in the street, and if not, by going to places like a shopping centre, or somewhere where it's cooler," retired Madrid resident Angela de la Vega told Reuters.