Twenty firemen fought the blaze, but were unable to pull the victims free.
The six were named as: Victoria Rainham, 18, who was the driver of the car, and Maria Tickner, 17, both of Orpington in Kent; Daniel Garwood, Stewart Innes, and Mark Higgins, all 17, and Daniel Spencer, 19, all of Eltham.
Police and fire experts yesterday resumed their investigation into Sunday night's accident. Post-mortem examinations were carried out at Greenwich mortuary and the cause of death was found to be asphyxiation.
Police believe the car span out of control just after 11pm as it went downhill, a wheel hitting the base of a traffic island. The car then struck the nearside kerb and span round before striking the pavement tree.
Scotland Yard said there was no suggestion that the vehicle had been stolen.
The scene shocked police, fire and ambulance crews. Traffic Sergeant Douglas Inglis said: "The scene was pretty horrendous - a burnt-out car with six people in it - I don't think it comes much worse."
Earlier yesterday Scotland Yard had appealed to friends or relatives of teenagers who failed to return home on Sunday to contact police.
Yesterday, bouquets marked the site, said by local residents to be a notorious accident blackspot.
Peter Bottomley, a former roads minister and the Conservative MP for Eltham, visited the scene.
He said: "For six people to die is one of the worst tragedies we've seen for very many years around here."