The first ever red weather warning for extreme heat has been issued over parts of Norfolk, which could cause a "potentially very serious situation".
The Met Office has now increased the warning to the highest level, which will see parts of west Norfolk and King's Lynn affected.
A national emergency has also been declared by the UK Health and Security Agency.
It comes as temperatures are predicted to soar to an eyewatering 40C across Monday, July 18, and Tuesday, July 19.
A red weather warning is only put in place when a heatwave is so severe and prolonged that it could impact the UK's health and social care system.
At this level, illness and death may occur among the fit and healthy, and not just in high-risk groups.
Grahame Madge, a Met Office spokesman, said: “We’ve just issued a red warning for extreme heat for Monday and Tuesday which is the first such warning ever issued.
“The warning covers an area from London up to Manchester and then up to the Vale of York.
“This is potentially a very serious situation.”
An amber weather warning will remain in place over the rest of the county on both days.
Dan Holley, a meteorologist at Weatherquest in Norfolk, said: "It is looking to be extremely hot.
"On Monday there will be highs between 37 to 39C in parts of Norfolk and temperatures will stay especially warm overnight.
"Into Tuesday morning, temperatures will rocket up to 39 to 40C plus and there could be a real danger to life."
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