The driver of a car which police believe was travelling with, or closely behind, the car involved in a fatal crash this morning has been urged to contact police.
One man died and another is fighting for his life after the vehicle they were travelling in collided with a bus in Lea Bridge Road, Leyton, at around 2.20am this morning.
Two passengers in the car were also injured during the crash involving a N38 bus bound for Whipps Cross, near Lea Valley Ice Rink.
They are described as being in a serious but stable condition in hospital.
Police say the driver of the second car could be a vital witness in the crash investigation.
The four men are believed to be in their early to mid-20s, but further details are yet to be released.
Ambulance crews also treated around 10 passengers who were on the bus.
Some of those were taken to hospital on another bus supplied by Transport for London.
They are believed to have suffered minor injuries.
London Fire Brigade crews also assisting at the scene.
There have been no arrests.
Roads around the scene remain closed between Chatsworth Road, at the junction of Lea Bridge Road, up to Orient Way.
A traffic island and a pelican crossing has recently been installed on the Claption side of the Lea Bridge and a bus lane is in operation on the long stretch of straight road.
Mateo Andres Castrillon, 18, was killed yards from the scene of the latest crash on Easter Sunday in 2012.
His motorbike was in collision with a car at the junction of Lea Bridge Road and Chatsworth Road.
The Serious Collision Investigation Unit at Chadwell Heath is investigating.
Anyone witnesses or anyone with information is asked to call the police non-emergency line on 101.