There were sweltering temperatures in parts of Britain today as the first heat-health alert of the summer came into force.
There were warnings that high humidity and a lack of breeze - even at night - could make life difficult for the elderly, young and those with underlying health problems.
Motoring organisations also warned drivers to give their vehicles a health check as breakdowns are likely to soar.
Temperatures recorded this afternoon placed Norwich as the hottest place in Britain with 30C (86F) recorded at its weather station.
Just behind was Writtle, in Essex, at 29.7C (85.5F).
St James' Park, in central London, and Gravesend, Kent, basked at 28.9C (84F).
Temperatures may go even higher across East Anglia and south-east England today and tomorrow but it is not the hot sunshine during the day that people need to be wary of, but roasting night-time temperatures of at least 20C (68F).
Wayne Elliott, head of health forecasting at the Met Office, said: "While there is the possibility of daytime temperatures reaching trigger thresholds, it is the night time values which are of real concern.
"High humidity and the lack of any breeze could make matters worse for people with underlying health problems."
The Met Office's heat warning is level 2 on its four level warning scale.
It relates to how likely temperatures will exceed "threshold" levels that trigger health concerns - typically 30C during the day and 15C at night.
The NHS advises to keep cool by wearing loose cotton clothes, spraying or splashing faces and the backs of necks with cold water several times a day and staying in the coolest rooms of the home as much as possible.
Windows should be kept closed when the room is cooler than it is outside.
Michelle Mitchell, Age UK charity director, asked people with an older relative or neighbour to check that they are coping with the heatwave.
"Our bodies are less able to cope with hot weather as we get older so it is extremely important that older people take sensible precautions during a heatwave, particularly if they are on medication," she said.
"During successive hot days it is important that older people are able to cool down in the evening and at night."
She suggested older people may wish to stay indoors or in the shade, keep homes shaded and well-ventilated, drink more non-alcoholic drinks, take cool baths or showers and continue to eat to replace the salt lost through sweat.
The Royal Society for the Prevention of Accidents (Rospa) today urged people to take care if cooling off in rivers and lakes and, where possible, to swim at properly-supervised sites.
Accidental drownings tend to increase during hot spells and Peter Cornall, head of leisure safety at Rospa, said: "River and lake swimming as part of a properly-organised activity is very different to the more ad hoc occasions when people take to the water to cool off, perhaps on the spur of the moment.
"If you choose not to go to a properly-supervised site, then think through the various hazards first and make sure you know what to do if anything goes wrong."
Breakdowns also increase in hot weather and the AA today reminded motorists to check their car's cooling system.
Steve Dewey, AA road operations director, said: "We tend to notice that for every degree above 23C, there is a noticeable increase in our breakdown workload, so very warm weather like this can sometimes double it.
"Overheating is a big risk, especially if you encounter any slow-moving traffic.
"If the worst happens and your car starts to overheat, turn on the air-conditioning and the heater up to full, then pull over," he said.
Drivers are also advised to carry drinking water, hats and sun cream in case of a breakdown.
The AA is putting on extra patrols especially on routes to the coast and to major events like the British Grand Prix at Silverstone, Northamptonshire, on Sunday.
The RAC said call-outs for reasons like running out of fuel and keys being locked in the car also increase when people are distracted as they plan a day out.
RAC Patrol Ambassador of the Year, Alan Wilcock, said: "I'd urge motorists travelling this weekend to ensure the journey is bearable for all passengers, especially children or pets.
"They may want to consider making their journey first thing in the morning or later at night when it is cooler, and less busy."
The RAC said no animal should be left in a car - even for a short period - on the warm day.
Chief forecaster at the Met Office Frank Saunders said there is a good chance of some places in East Anglia and south east England reaching 32C but it won't be hot everywhere with cloud and some rain expected over northern regions of the UK.
The north west of England, west Wales, Scotland and Northern Ireland will be the coolest spots over the weekend, temperatures only reaching the high teens and low 20s.
The highest temperature reached so far this year was 30.9C (87.6F) in Gravesend, Kent, on June 27.