The two men, believed to be father and son from Essex, were killed when the private aircraft crashed into a field shortly after take-off, police said.
The five-seater Bell 206 Jet Ranger experienced problems near the village of Cudham, south London, before crashing.
Villagers later praised the pilot for avoiding hitting any houses and putting more people in danger.
'Obviously dead'
A 20-year-old man who did not want to be named said: "By the time we got up to the scene there were already two people on the grass. They were obviously dead.
"The person that was flying, swerved round all the houses and hit a field.
"He was trying to crash land somewhere. God rest his soul, he tried his best."
Another villager said: "It deserves to be reported that the person obviously tried very hard to miss people's houses and the residential part of the village."
Safety record
The men had flown from Biggin Hill Airfield and were on their way to Southend in Essex when they crashed.
Witnesses described seeing the helicopter circle twice in a desperate bid to gain extra height before it disappeared into the clouds.
"They then saw the helicopter pitch out of the sky and crash to the ground," said Chief Inspector Geoff Matthews, from Bromley Police station.
Emergency crews were immediately despatched to the scene which was being preserved by police officers ahead of an investigation by the Air Accidents Investigations Branch.
A Biggin Hill spokeswoman said: "It is far too early to say what may have caused the crash but everyone here is very upset about it.
"Thankfully situations like this are very rare. The airport has an exemplary safety record."