The incident happened in Rainham Road South at around 5.45am today (September 10).
London Fire Brigade crews were returning to station from another incident when they received the call and arrived on scene.
Firefighters provided immediate emergency care to the pedestrian before colleagues from the London Ambulance Service took over.
Two other people were also treated at the scene by emergency crews.
The pedestrian was taken as a priority to a major trauma centre where their condition is unknown.
The two other patients were assessed and discharged at the scene without needing further hospital treatment.
In total, two fire engines from Dagenham Fire Station attended alongside ambulance crews and a paramedic in a fast response car.
The A1112 Rainham Road South was closed in both directions between Crown Street and Sandown Avenue following the crash.
It has now reopened.
We have contacted Metropolitan Police for further details on the incident.
