Firefighters are unaware of the full extent of the damage caused by blazes which affected houses, schools and churches across London, with crews describing scenes as “absolute hell”.

Residents were being evacuated from their homes and people were taken to hospital amid fires in the capital as temperatures soared to more than 40C on Tuesday afternoon.

Two “large-scale” incidents took place in Upminster and the village of Wennington, east London, where black smoke billowed into the air, while flames destroyed buildings and ravaged nearby fields.

Several other significant incidents also occurred, with people urged not to have barbecues or bonfires due to the “unprecedented” challenges crews face.

A firefighter at the scene in Wennington, asked by the PA news agency what conditions were like, replied: “absolute hell”, while those affected by the blaze said it had been spreading “fast”.

Two people were also taken to hospital suffering smoke inhalation following a fire in Dagenham, with the full number of casualties unknown.

London Fire Brigade (LFB) declared a major incident due to “a huge surge” in blazes across the capital.

Jonathan Smith, assistant commissioner at LFB, told the PA news agency: “We’ve had a range of incidents today, obviously a number of which have been the result of the tinderbox dry woodland and grassland both in central London and in the suburbs.

“This has caused rapid fire spread which has impacted on properties, people’s homes, schools, churches and other types of buildings.

“At the moment, because of the sheer number of incidents we’ve been attending today, we will be pulling all of that information together and making sure every incident is thoroughly investigated.

“Once we’ve done that we’ll be able to give an accurate picture of exactly the incidents we’ve attended, how many homes have been affected and if there have been any casualties.”

He said that Tuesday evening would be “critical” in ensuring the fires are kept under control, adding: “It would be premature to say we are out the other end of this incident”.

The London Ambulance Service said the total number of people taken to hospital may not be known until Wednesday morning.

Sadiq Khan said LFB had received more than 1,600 calls for assistance by late Tuesday afternoon.

He also said people should not be having barbecues anywhere in London, including in parks and private gardens – as well as on patios and balconies.

In Wennington, local residents could be seen being comforted, while others were seen removing gas canisters from a nearby pub, as hundreds of firefighters were at the scene.

At least one home could be seen completely destroyed by the fire, while others appeared to be badly damaged Local resident Janet Hickey, 70, who has terminal pancreatic cancer, said she was forced to leave all her cancer drugs behind as they were evacuated.

Her husband Patrick Hickey, 71, added: “We had to leave everything.

“We’re hoping against hope that our house is still there.”

A rescue centre has been set up at the Wennington Premier Inn for residents who have been evacuated.

Riminta Maceikaite, 38, and her son Nikas Janulevicius, 13, said their neighbours’ homes have burned down but as far as they can see from TV aerial shots, their house is still standing.

Lizzie Pittman, from Aveley in Essex, who works at some stables by the roundabout, said she was looking after five horses that were evacuated.

She said: “This is your worst nightmare. You can see it getting closer and closer. People are losing their houses but that’s bricks and mortar. People are losing their livestock.”

Nearby resident, Lynn Sabberton, who said she was evacuated from her home with her partner who has a lung difficulty, told Sky News:“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.”

Freya Gutteridge, 23, from nearby Hornchurch – who works in marketing, told PA:“We’re all really worried, the wind is strong and we’re seeing on the news that loads of houses are on fire and there isn’t enough fire engines.

“It’s crazy. Most of us in the office live really locally so we’re all worried about families’ houses at the moment.”

It was among the fires being tackled in London on Tuesday afternoon, which were:

– 30 fire engines dealing with a grass fire on Pea Lane in Upminster.

– 12 fire engines tackling a fire involving garden fencing and trees on Uxbridge Road in Pinner.

– 10 fire engines tackling a restaurant fire on Green Lanes in Southgate.

– Eight fire engines tackling a grass fire on Oaks Road in Croydon.

– Eight fire engines tackling a grass fire on Ballards Road in Dagenham.

– Eight fire engines tackling a fire on The Broadway in Wembley.

– Six fire engines tackling a grass fire on Sunningfields Crescent in Hendon.

– Four fire engines tackling a grass fire on Chapel View in Croydon.

– Four fire engines tackling a fire on Sidcup Road in Eltham.

Houses were evacuated in Dagenham following a “significant grassfire” which affected a number of buildings and left a man and woman in hospital due to smoke inhalation.

London Mayor Sadiq Khan said on Twitter: “This is critical: @LondonFire is under immense pressure.”

He also said: “We simply can’t cope with the number of fires across our city directly attributable to the heatwave we’re experiencing, the dry grass, the way the fire spreads during the heatwave.”

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