The Met Office has issued a Heat-health alert for parts of England as temperatures are set to rise over the next few days.
Warning of potential Heat-Health Watch conditions, the alert covers London, the South East, East of England, and both East and West Midlands.
It has been issued as hot air from the continent is set to move north to the UK over the coming days, with the potential for parts of the south east to see temperatures in the low 30s Celsius.
Night time temperatures are also likely to be well above average, with some places seeing overnight minima around 20 Celsius.
Steve Ramsdale, Deputy Chief Meteorologist at the Met Office, said: "Hot and very humid air coming up from the Spanish plateau will see some particularly high day and night temperatures as we head into the weekend.
"The humidity will make it feel close, muggy and uncomfortable for many in the heat and people should take steps to keep cool - particularly across the areas where we have issued a heat health alert."
Dr Paul Cosford, director for health protection at Public Health England, said: "While many people enjoy hot weather, high temperatures can be dangerous, especially for people who may be particularly vulnerable such as older people, young children and those with serious illnesses.
"During the day take care in the sun, don't over-exert yourself in heat, drink lots of cool fluids and keep an eye out for friends and neighbours, also do what you can to minimise your risk of a sunburn and try to keep sleeping areas cool."
Met Office meteorologists are also keeping a very close eye on the potential for widespread heavy thunderstorms on Saturday from what is known as a 'Spanish plume'.
A 'Spanish plume' is a term which describes a complex set of conditions where warm air from the continent is forced to rapidly rise when it meets cooler air from the Atlantic.
If this happens over the UK with the right conditions in the upper atmosphere, it can set off violent thunderstorms with the potential for some intense downpours and hail.
Andy Page, Chief Meteorologist at the Met Office, said: "There is potential for some intense thunderstorms on Saturday which could see large rainfall totals in a short space of time, which can cause flash flooding, as well as lightning and large hail.
"However, there are a lot of factors that have to come together to set off this situation, so it remains a risk rather than a certainty at the moment. Our meteorologists will be monitoring this around-the-clock as the situation develops and we encourage everyone to stay up-to-date with the latest picture through our UK forecast and Severe weather warnings."