A man has been arrested on suspicion of driving a car the wrong way down a motorway after a serious crash.

A woman has been taken to hospital with severe injuries following the smash, which happened between junction 11 and 10 just after midday.

The motorway was closed in both directions, but one lane of the coast-bound carriageway reopened at 3pm. Now the motorway has been reopened in both directions, but there are still delays as traffic has built up on the M20 and on the A20.

Scroll down for audio

Now one driver, who was caught up in the incident, has described the moment he saw a car coming straight at him the wrong way.

The man, who wants to be known only as Paul, was driving to Ashford rail station in lane three.

There was a lorry in lane one and another car overtaking in the middle lane.

Paul said he saw a car coming straight at him after a bend.

He said: "I kind of had to do a double take. I thought I was seeing things."

He said luckily the car he was overtaking braked.

Paul then rang 999.

Police have since launched an appeal for anyone who saw the incident, or the vehicles involved beforehand, to come forward.

Officers were called to reports of a black Seat Leon travelling the wrong way on the London-bound carriageway.

It then collided with another car, causing serious injuries to a passenger.

The driver allegedly seen travelling against the flow of traffic in the outside lane suffered minor injuries.

He has been arrested on suspicion of causing serious injury by dangerous driving.

Police Constable Simon Masterson from the serious collision investigation unit said: "There will be a number of people who would have seen this incident, and potentially might have video footage from dash cams.

"I would appeal for anyone who has any information that they think could be relevant to call us as soon as possible."

Three ambulances were sent to the scene, as well as air ambulance crews, police and the fire brigade.

Fire crews say they used cutting equipment to free a motorist from the wreckage of one of the vehicles involved.

Ambulance spokesman Rich Airey said one woman was cut free after being trapped in the vehicle "for some time". She was then taken to hospital with multiple injuries, but in a stable condition.

Two others were taken to the William Harvey Hospital in Ashford, one with a possible broken leg and the other with a hip injury.

The road is expected to remain closed until after 4pm today.

Diverted traffic is told to follow the hollow square symbol via the A20.

KCC Highways is urging motorists leaving the Port of Dover to use the M2 and A2. A spokesman said trapped traffic will be released as soon as possible.

Anyone with any information is asked to contact the serious collision investigation unit on 01622 798538 or email sciu.td@kent.pnn.police.uk.