The police confirmed that two people were dead at the scene and nine others had been injured, five of whom were treated for minor injuries. The pilot of the helicopter was among those dead. (Read More Below Video.)
The BBC, quoting Metropolitan Police Commissioner Bernard Hogan-Howe, said one person was "critically ill".
Police and the London Fire Brigade rushed to the scene of the crash near Wandsworth Road in South Lambeth.
CNBC's Tom Mackenzie reported the crane was attached to a 50-floor high building and that two cars were badly burnt and debris was spread across the road. There are concerns about the stability of the crane, which dangled from the side of the building, and engineers are expected to inspect it shortly.
It is not known how many people were on board the aircraft.
The crash happened during foggy weather conditions Wednesday morning, close to the London Heliport in Battersea, the closest helipad to central London.
Users on Twitter shared pictures of the crash, which happened during morning rush hour. The incident caused major traffic and transit disruptions.
Calls to the London Heliport were not returned.
- CNBC's Tom Mackenzie contributed to this report.
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