Public Health England (PHE) is urging people to stay cool as temperatures soar and has reminded them not to leave children or animals in parked cars.
Owen Landeg, principal environmental public health scientist at PHE, said: "Much of the advice on beating the heat is common sense and for many people spells of warmer weather are something they very much enjoy.
"However, for some people, such as older people, those with underlying health conditions and young children, the summer heat can bring real health risks.
"That's why 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 support. Also take water with you when travelling and keep up to date with weather forecasts.
"It's also worth remembering to think about practical steps to keep homes cool during the day as this can aid sleeping at night and give the body time to recover from the heat."
In its top tips, PHE said people can shade or cover windows that face the sun to keep indoor spaces cooler.
People should also drink plenty of fluids, avoid excess alcohol and open windows when it feels cooler outside and if it is safe to do so.
Nobody should ever be left in a closed, parked vehicle, especially infants, young children or animals, it added.
And it said people should avoid the sun between 11am to 3pm but, if they do go out, they should walk in the shade, apply sunscreen and wear a hat.
Other tips include avoiding physical exertion in the hottest parts of the day and wearing light, loose-fitting cotton clothes.