There is severe congestion on the A507 around Henlow, Arlesey and Stotfold after a crash involving six vehicles.
Nobody is thought to have been seriously injured in the incident, to which emergency services were called at about 3.40pm.
Crews remain at the scene, but the road is open.
An ambulance service spokeswoman said: “We sent two ambulances, a volunteer first responder and a paramedic officer, and we assessed four patients before the ambulances left the scene. It doesn’t look like there are major injuries, thankfully.”
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