The A507 near Baldock is closed in both directions due to a “serious collision”.
Police are currently on the scene of the crash, which happened at the junction with Warren Lane and Ashanger Lane.
The A507 has been closed between Baldock and Cumberlow Green to allow emergency services to work at the scene.
A police spokeswoman described the crash as “serious”, and said the closures are likely to be in place for several hours.
Motorists are advised to avoid the area this evening and take alternative routes where possible.
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