The incident happened between junctions 29 and 30 on the anticlockwise carriageway just after 8.50am today (March 18).
Emergency services attended and found three injured with one person trapped in a vehicle.
The person was rescued and all three were taken to hospital where their conditions are being assessed.
Closures were put in place as the incident was dealt with which caused severe delays.
All diversions have since been lifted with traffic returning to normal.
A spokesperson for Essex Police said: “We are at the scene of a collision on the M25 between junctions 29 and 30 on the anti-clockwise carriageway.
“It was reported three vehicles were involved in a collision at about 8.50am, leaving one person with injuries and another person trapped in their vehicle.
“Paramedics attended the scene and treated one woman, and firefighters attended the scene and freed another person from a vehicle.
“The road remains partially blocked while emergency services make the scene safe.
“Drivers should check before they travel and plan their journeys accordingly.”
An East of England Ambulance Service spokesperson said: “We were called just after 8.50am to a road traffic collision involving multiple vehicles on the M25 near South Ockendon.
“Three ambulances and an ambulance officer vehicle were sent to the scene.
“Three patients were transported to Basildon University Hospital for further assessment and treatment.”
