Emergency services were called to an incident at Corfe Castle.
Paramedics treated a man that had reportedly fallen unwell in a lorry parked in a layby off the A351 Gallows Hill.
He was airlifted to Southampton General Hospital for treatment.
Police were also called to the scene.
A spokesman for Dorset Police said: "We were called at 12.33pm today by the ambulance service.
"The road was partially blocked while paramedics treated the man."
The A351 is now clear following the incident.
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