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.
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