People are being urged to “stay out of the sun” for most of this week, as a heat health watch alert is issued by the Met Office.
The level 3 or amber alert is in place until 09:00 BST Friday for much of the east and south-east of England.
The hottest day of the year has been recorded in Santon Downham in Suffolk, which reached 33.3 C on Monday (92F).
The National Farmers’ Union has warned of crops “parched to the bone” and livestock farmers using winter rations.
The level 3 warning is issued when temperatures are predicted to hit 30C during the day, and 15C at night, for at least two consecutive days.
In the affected areas there is a 90% probability of heatwave conditions, the Met Office said.
It is the third time the level 3 alert has been reached in England this year.
The alert is different to the severe weather warnings issued throughout the year for snow or rain.
Operating in conjunction with Public Health England, the heat health watch service helps keep health professionals and people working in social care prepared to keep people safe.
“We advise the public to take care in the sun, especially when temperatures are potentially reaching 30 degrees or more throughout this week – either stay out of the sun or be sensible and don’t go out in the strongest sunshine hours – 11am to 3pm,” the Met Office spokeswoman said.
The public were urged to take the usual precautions in the sun, including covering up, wearing sun screen, keeping your house cool and drinking plenty of water.
Several parts of the country have had 54 consecutive dry days, according to the Met Office, which defines a dry day as one where less than 1mm of rain falls.
The longest run with no rain at all has been 48 days at Brooms Barn, near Bury St Edmunds. The Met Office said most of its weather stations in East Anglia have had no rain at all since 21 June.
Guy Smith, deputy president of the National Farmers’ Union said crops were “being parched to the bone”.
“Spring crops that farmers sowed in April barely knowing what rain is,” he told the BBC.
“As you travel west… a little bit more rain but even here the grass has stopped growing and that’s a problem for livestock farmers because they need to have that grass growth to sustain their sheep and cows through to the winter.
“We’re hearing that livestock farmers are now having to feed winter rations to their stock and that’s going to cause problems later on.”
‘The Sussex savannah’
Mr Smith said vegetable farmers also face problems as their reservoirs – used for irrigation – begin to run dry.
“If this weather continues…we will see impacts on vegetable production. The signs are ominous.”
David Exwood runs Westons farm in West Sussex, and said his yields are down by 25%.
“Crops are suffering, the fire risk at the moment is exceptional,” he told the BBC.
“It’s the Sussex savannah at the moment. I mean the cracks in the ground are extraordinary, they go down over a metre and so it’s going to take a lot of rain to turn this around.”
Meanwhile, the Woodland Trust has warned wild berries are ripening early, which could lead to them being smaller or dropping from trees and shrubs.
“We’re already anticipating signs of autumn,” said Dr Kate Lewthwaite from the Woodland Trust.
“Although we’ve only had a small number of berry records so far, the heatwave will only encourage more fruit to ripen, and leaves on trees may also start to change colour.”