Firefighters tackling blazes which have ripped through homes and buildings in London have described the conditions as "absolute hell", on what is the UK's hottest day on record.
Residents were evacuated, people were taken to hospital and a major incident was declared by the London Fire Brigade (LFB) which was "under immense pressure" following after a "huge surge" in fires across the capital.
Mayor Sadiq Khan described the situation as "critical" and said people should not be having barbecues anywhere in London today and tomorrow, including in parks and private gardens, as well as on patios and balconies.
He told Sky News: "It's not about us being the nanny state or party poopers, it's the reality of accidents happening and fires starting and spreading rapidly, in your garden, decking, homes and so forth," adding people should not be 'wild swimming' during the heatwave.
Mr Khan went on to say that on a normal day, the London fire service receives a total of 300-350 calls for help, but today they have had more than 1,600 by late afternoon.
Dozens of fire engines and hundreds of firefighters have been involved in tackling at least 10 separate blazes today.
In the village of Wennington on the outskirts of east London, several houses were destroyed and others were severely damaged after grass fires broke out, engulfing properties, as black smoke billowed into the air.
LFB sent 15 fire engines and about 100 firefighters to the area to deal with blazes that covered a number of buildings and grassland.
Aerial footage showed smoke covering the village and approaching a historic church.
Asked what conditions were like, a firefighter at the scene replied: "Absolute hell".
Meanwhile, two people were taken to hospital suffering smoke inhalation following a separate fire in Dagenham.
Sky correspondent Laura Bundock, reporting from the site in Wennington, said: "The smoke in the air is really, really thick. It was like night fell as we drove towards the village, as we came closer to the fire.
"The ground here is tinder dry, it is brittle. Walk underfoot and it crunches underneath. So any fire, any wind is going to make this spread even further."
Nearby fields were completely scorched and burning intensely. It is not known if anybody was hurt in the incident and the cause is unclear.
Elsewhere in the UK, the Leicestershire fire and rescue service has also declared a major incident "due to high demand", saying: "We will not be attending automatic fire alarms. Please only call us if it's an emergency."
100 firefighters battle blaze
LFB, which declared the major incident in London, tweeted: "We've got 15 fire engines and around 100 firefighters dealing with this blaze on The Green in Wennington."
The houses were burning close to a fire station in the village, understood to be home to around 300 people.
Pierre L'Aimable, who witnessed the fire, said it was "immense... there was so much black smoke in the air".
He told Sky News: "There are horse stables nearby and we saw those horses being evacuated, and people being evacuated. There are loads of animals being saved."
'A lot of people distressed'
Mr L'Aimable said a lot of people were evacuated from homes.
"You could see a lot of them were near the fire because there was black on their chests so they were very close to it. A lot of them were distressed unfortunately."
Lynn Sabberton, a resident, who said she was evacuated from her home with her partner who has a lung difficulty, told Sky News: "We thought it was one of the fields that caught alight over the back of us.
"But then a neighbour rang me and said, 'oh no, it's on the green, the green has caught fire'."
The fire 'spread so quickly'
Ms Sabberton continued: "I saw the black smoke and the helicopters came over and more police came into our neighbourhood and it was really spreading very fast.
"It just spread so quickly, I think the wind caused the fire to go our way towards the village."
She said she believed her home was "safe at the moment" but her husband's condition was "not very good" as he did not have time to bring his inhaler with him.
It has been the hottest day on record in the UK, with provisional Met Office figures showing the temperature hit 40.3C in the village of Coningsby in Lincolnshire, beating the previous record of 38.7C (101.66F) registered in Cambridge three years ago.
At least 34 weather monitoring stations have exceeded the old UK record, and five have equalled it.
Scotland also provisionally recorded its highest-ever temperature on Tuesday.
It hit 34.8C (94.6F) in Charterhall in the Scottish Borders, beating the previous record of 32.9C (91.2F) recorded in Greycrook in August 2003.
As well as the major fire in Wennington, there were also a number of other blazes today elsewhere in London:
• Thirty fire engines were dealing with a grass fire on Pea Lane in Upminster
• Twelve fire engines were tackling a fire involving garden fencing and trees on Uxbridge Road in Pinner
• Ten fire engines were attending a restaurant fire on Green Lanes in Southgate
• Eight fire engines were tackling a grass fire on Oaks Road in Croydon
• Eight fire engines were dealing with a grass fire on Ballards Road in Dagenham
• Eight fire engines were attending a fire on The Broadway in Wembley
• Six fire engines were tackling a grass fire on Sunningfields Crescent in Hendon
• Four fire engines were dealing with a grass fire on Chapel View in Croydon
• Four fire engines were attending a fire on Sidcup Road in Eltham.
The London Ambulance Service said its crews were "responding to a number of fire incidents across London including at Rainham and Wembley".
"We have a number of resources on scene including ambulance crews and our Hazardous Response teams. We are treating patients on scene."