According to National Highways, a car had “gone over the central reservation barrier” during the collision. The motorway has been closed between junction 20 and junction 21.
National Highways north-west gave an update about the traffic situation on Twitter.
It said: “The M6 is closed in both directions between J20 (M56) and J21 (Warrington) following a serious collision involving a car that has collided and gone over the central reservation barrier. Emergency services and Traffic Officers are on scene.”
Others took to Twitter to discuss the situation at the scene.
One user said they had seen one vehicle “through the central reservation and one upside down.”
Another added that they had seen what “must be a dozen” ambulances passing the scene.
North West Ambulance Service confirmed that there are four patients who would be taken to hospital for minor injuries.
It said: “We were called at 13.55 to reports of an RTC. We sent three ambulances, a rapid response vehicle, our Hazardous Area Response Team and an air ambulance.”
National Highways warned of “heavy congestion” up to four miles long and delays of approximately 60 minutes.
It said in an update: “There are delays of 60 minutes above normal travel time northbound with 4 miles of congestion on approach to J20. There are also 45 minute delays above normal travel time southbound with 4 miles of congestion on approach to J21.
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The traffic monitoring website Inrix gave an update at approximately 3.30pm that all but one lane of the M6 Northbound were open while the M6 Southbound was still closed.
Transport for Greater Manchester tweeted at 4.28pm that traffic on the M6 was causing severe delays on nearby roads.
It said: “Due to traffic diverting after a serious incident on the #M6 severe delays are being experienced on the #M56 #M60 #M61 and surrounding routes.
“Please postpone your journey or avoid travelling via these routes if possible.”