A 81-year-old woman was airlifted to hospital in Carlisle with potentially serious chest injuries following a two-car crash on the A596.
Traffic was brought to a standstill at about 2.40pm and the road was closed for several hours between Iggesund Paperboard and Lowca Lane.
It has since reopened.
Emergency services arrived on scene before crash investigators arrived at around 4pm.
Fire crews rescued one of the casualties who was trapped. They used hydraulic equipment and small tools.
The woman was assessed on scene by air medics from the Great North Air Ambulance Service and was in a stable condition on arrival at hospital.
A police spokesman said: "The road was closed in both directions and diversions were in place at Lowca Lane.
"Motorists were advised to take care on the diversionary route and adapt their driving accordingly.
"Motorists are asked to avoid the area and use alternative routes."
Most traffic is diverting through Seaton.
The road reopened at about 9pm.
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