A heat health warning for parts of England has been upgraded from yellow to amber by the UK Health Security Agency.
Temperatures are expected to reach 30C in parts over the weekend, making it hotter than Marbella, Ibiza and Tenerife as a "plume of warm air" moves in from the south.
The initial alert was issued on Wednesday for six regions of England, London, the East Midlands, West Midlands, East of England, South East and South West.
On Thursday the warning was escalated for the West Midlands, East Midlands, East of England, South East and South West, and the amber level means the impact of the weather is "likely to be felt across the whole health service... and the wider population, not just the most vulnerable".
The UKHSA further issued a yellow alert for the North East, North West and Yorkshire and Humber regions.
All alerts are in place between 9am on Friday and 9am on Monday June 12.
It comes as large parts of England and Wales have been issued with a thunderstorm weather warning by the Met Office.
The UK's weather service issued the warning on Thursday ahead of what is expected to be the warmest weekend of the year, with central and southern England, and the whole of Wales, set for rain and thunder on Saturday.
The warning comes after weeks of prolonged high pressure which has led to the recent sun and high temperatures but as the high pressure moves north, the UK is expected to see higher temperatures as well as thunder, hail and rain hit central and southern England and Wales.
A change in weather is expected to come at around 2pm on Saturday, with the warning in place until 9pm on Saturday.
Oli Clayden, from the Met Office, confirmed that there could be some travel disruption over the weekend.
He said: "After a prolonged dry spell there is a chance of surface water flooding.
"There could be some surface water issues that could cause travel disruptions as well as the high gusts across parts of the country."
It is expected that some parts of the UK could see 30-40mm of rain in an hour during parts of Saturday, with hail also expected to hit the UK on Saturday.
Temperatures are forecast to increase steadily heading into the weekend, with Saturday expected to see temperatures rise to as high as 30C in southern parts of England before they slowly decrease in the days that follow.
Mr Clayden added: "This is going to be the warmest weekend of the year, which is to be expected as we go into summer.
"This weekend will also see hail mixed in with strong gusts of wind and rain hit parts of the country."
