Residents in Hackney told ITV News London they heard two loud bangs before seeing a man "on fire in the street".
The man, who is in his thirties and was working nearby in Mare Street, is fighting for his life in hospital.
Four fire engines and around 20 firefighters attended the scene at around 12:15pm.
The blaze, which also damaged the ground floor of a nearby shop, was brought under control after just over an hour.
An "exploding" van that set on fire in Hackney this afternoon is "not terrorist-related," Metropolitan Police have said.
The van and a property are believed to have set on fire as a result of works carried out near a generator inside a commercial property at around 12:15pm, police said.
A man in his thirties - believed to be a worker at the property - suffered serious burn injuries in the incident and is in a critical condition at an East London hospital.
There are no other reported injuries.
One person has been taken to hospital following a fire on Mare Street, Hackney, the London Fire Brigade said on Twitter.
Four fire engines are still at the scene after a van and building set alight.
The road is closed in both directions.
Van on fire on Mare street - man laid out on floor. Ambulances rushing to scene now, junction of Brenthouse road. http://t.co/Dh0KzEFalC
Emergency services are attending the scene of a fire in Mare Street, Hackney, after a van set on fire.
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A motorcyclist has died in a crash with a cyclist in Hackney, east London according to reports.
Two men collided as they travelled along Green Lanes, close to Clissold Park, at 4.20pm yesterday, the Evening Standard reported.
The motorcyclist, who was pronounced dead at the scene by London Ambulance Service paramedics, was believed to be in his late 20s.
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Police in Hackney Borough are continuing to appeal for the public's help in locating a missing teenage girl from Hackney. Detective Sergeant Paul Ridley, from Hackney Borough CID, said:
"Houceline has not been seen now for several days. The weather is becoming much colder. I am extremely concerned regarding her welfare. Her disappearance is out of character. Her family are very worried."
Houceline Nzumba, 16, was last seen at around 16:30hrs on 13 November leaving the BSix Sixth Form College, Kenninghall Road, E5. She is described as a light skinned black girl of Congolese origin. She is tall with a slim build, and has short black hair.
She was last seen wearing black jeans, a black jumper with the word ‘Geek’ written in white writing across the front, light brown Timberland boots, a green waist length puffer style jacket and was carrying a black handbag with a gold crown on it.
Houceline regularly uses the public transport network and has links to Tottenham area.
Anyone who has seen Houceline or who knows of her whereabouts are asked to call the CID on Hackney Borough via 101.