Traffic has piled up on Townwall Street, the A20, following a collision involving a car and a lorry.
The incident happened around 12.35pm where the lorry began leaking a chemical substance from its cargo onto the road.
Diversions were in place for more than two hours while the area was secured.
First on the scene were fire-fighters equipped with breathing apparatus.
They used environmental protection packs to prevent further leaks.
Passers-by and motorists are not at risk.
Police came just after 1pm and were joined by Port of Dover police.
A spokesman for Kent Police said:"Officers from Kent Police, the Port of Dover Police and KFRS are on scene and traffic diversions are in place whilst the scene is cleared."
It is believed that there are around five fire engines at the scene as well as four police vehicles.
Traffic is said to go beyond Dover Leisure Centre and up to the entrance of Jubilee Way.
Resident, Bill Beer, was passing when he saw the commotion, he then took it upon himself to investigate.
He said: “I was down there and spoke to the police on duty.
“It was a chemical spilling from drums on a Polish lorry heading towards the docks.
“Apparently they were having to remove the drums, containing some kind of toxic chemicals, from the back of the truck.
“The police did not know what the chemical was, except that it was clear in the drums and tuned blue when it spilled out, and is toxic to marine life, so had to be dealt with before it could get into the drains.”
Resident, Gary Pullen managed to capture some footage of the scene, uploaded to Facebook.