A heat-health alert has been issued for parts of the UK as temperatures are predicted to hit 30C (86F), higher than in Los Angeles, Marbella and Santorini.
The alert was raised earlier to level 3 and people are asked to check on those vulnerable to extreme heat.
Friday marked the first in a predicted run of days of consistently high temperatures in south and east England.
Heatwaves are becoming more likely and more extreme because of human-induced climate change.
A high of of 28.5C was recorded in St James’ Park in London on Friday.
BBC weather forecaster Gemma Plumb said temperatures would continue to climb over the weekend.
“Most of the UK is set to turn warmer this weekend and into the start of next week, with temperatures for much of England and Wales into the high 20Cs or low 30Cs,” she said.
She added that there were indications the weather would likely turn cooler for a time around the middle of next week.
“However, there is the potential for hot weather to push back up from the south across parts of the UK during next weekend and early the following week,” she said.
A UK Health Security Agency (UKHSA) warning will be in force from Monday 11 July until Friday 15 July for affected areas.
The agency suggests people shade or cover windows exposed to direct sunlight, check fans and fridges are working properly, and that medicines are correctly stored.
“We want everyone to enjoy the hot weather when it arrives, but also to check in on their vulnerable family, friends and neighbours,” the UKHSA’s Dr Agostinho Sousa said.
The Met Office declares a heatwave when it records at least three days in a row with maximum temperatures exceeding a set temperature – which varies in different areas of the country.
When the heatwave temperature thresholds are passed, the weather service issues a heat-health warning which is sent to health and social care professionals so they can take action to minimise the impact of the heat on people’s health.
How are you preparing for the heatwave? Get in touch.
The UK previously experienced a heatwave three weeks ago, with 17 June marking the hottest day of the year so far.
Northern Ireland had its hottest day of 2022 so far on Thursday, with highs of 23.5C.
BBC Weather presenter Nick Miller said: “Temperatures are set to rise this weekend lasting into at least the first half of next week.
“Parts of England and Wales will see highs in the upper 20s and low 30s Celsius for several days and meet the criteria for an official heatwave to be declared.
“Some places are likely to see their highest temperature of the year so far.”
Scotland could see highs of 23C in the next few days.
The world has already warmed by about 1.1C since the industrial era began in the latter half of the 18th century, and temperatures will keep rising unless governments around the world make steep cuts to emissions.
In England, there were 2,500 excess deaths in the summer of 2020 as a result of hot weather, while heat-related deaths in the UK could treble in 30 years, the British Red Cross predicts.