Kent Police responded to reports of the crash on the coastbound A2.
Officers arrived at the scene, along with paramedics and Kent Fire and Rescue Service.
One person has been reported injured.
The incident, which occurred at 3.27pm between the M25 junction and the Bean junction, brought traffic to a standstill on the A2 coastbound.
Three fire engines attended, with crews assisting paramedics.
All lanes have since reopened, but there are still residual delays of up to 55 minutes, with congestion stretching back towards the M25 Junction 2.
A spokesperson for Kent Police said: “Kent Police was called to the A2, coastbound at Dartford following reports of a collision involving three vehicles.
“Officers attended, along with SECAMB and KFRS.
“One person has reported injuries.
“One lane is open.”
