The emergency services are currently at the scene of a crash on the A41 Aston Clinton bypass.
It happened at around 9.50am and involves a car and tanker lorry.
The incident happened on the northbound carriageway.
The road is currently closed in both directions.
South Central Ambulance Service described the collision as ‘serious’ and sent a paramedic team leader in a rapid response vehicle and an ambulance to the incident.