Ambulances and an animal charity have been inundated with calls as Britain swelters on the hottest day of the year so far.
Temperatures have topped 30C in the North East today - making it hotter than swathes of Europe - but the hot weather has led to a surge in emergency calls.
The Met Office has declared a Level 3 heatwave alert and Public Health England is urging people to take care.
But the thermometers and humidity levels should fall tonight when heavy, thundery showers sweep across the UK. The Met Office has issued a yellow weather warning for severe storms, large hail and strong winds which could lead to flash flooding of homes, businesses and transport networks.
"The risk of thunderstorms coming across from Northern Ireland later on this evening, and then spreading across Scotland and then also further south across Wales and northern England, and also western parts of England - a big chunk of the UK - as we go through tonight and into tomorrow."
The North East forecast:
This Evening and Tonight
Dry, hot and humid tonight with clear skies at first. Cloud developing through the night with heavy thundery showers, hail and occasionally gusty winds from the early hours. A fresh breeze along the coast. Minimum Temperature 21C.
Staying warm and humid with heavy, thundery showers, gusty winds and a chance of hail affecting some areas. Turning drier later in the evening. Maximum Temperature 24C.
Outlook for Thursday to Saturday
It will feel a little fresher from Thursday with temperatures closer to normal. Sunny periods and isolated showers, with these most likely on Friday.
Dr Angie Bone, head of extreme events at Public Health England, said: "Now the heatwave has arrived people will likely be out and about more enjoying the summer sun.
"But it's important to remember that there are some people whose health suffers in hot weather. Older people, those with underlying health conditions and young children may all feel the ill-effects of heat over the coming days.
"We're urging everyone to keep an eye on those you know who may be at risk this summer. If you're able, ask if your friends, family or neighbours need any help."
The RSPCA has seen a spike in calls from members of the public concerned about dogs left in hot cars, conservatories, sheds and caravans.
Inspector Justin Stubbs said three dogs had already died this summer after being left in cars.
Met Office forecaster Alex Burkill said: "I there's a fairly good chance that we'll see 35C today somewhere. Yesterday was the hottest day of the year so far and we only reached 30C yesterday, so it is going to be the hottest day of the year so far I can say with a pretty good degree of confidence.
"It's not going to be the hottest day for too far back - we reached 36.7C (98F) on July 1 last year so it will be the hottest day for over a year, but not the hottest July day ever."