All three victims were declared dead at the scene in Rainham, east London, on Monday night.
Three people have been killed after their car hit another vehicle that had been brought to a halt by a previous crash minutes earlier.
Police had been called to the initial collision in Rainham, east London, shortly after 10pm on Monday.
But before officers reached the scene on the A13 close to the Rainham Marshes Nature Reserve, another car smashed into one of the vehicles involved.
All three victims were declared dead there a short time later.
A fourth person was taken to hospital but has since been discharged.
No arrests have been made.
The incident took place within the Metropolitan Police area but close to the border with Essex Police.
Calls to the first collision were answered by Essex’s control room and the Met picked up those for the second.
Both forces have made referrals to the Independent Office for Police Conduct.
Detective Inspector Julie Trodden, from the Met’s Serious Collision Investigation Unit, said: ‘This is an extremely tragic incident, and my thoughts remain with the families of those who lost their loved ones.
‘We are keen to speak with anyone who may have been driving along this stretch of road around 10pm on July 15 and who may have dashcam footage of the incident.’
Officers attended the scene along with the East of England Ambulance Service and the London Fire Brigade.
The next of kin of those who died have been informed and are being supported by specialist officers.
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