A person is in a critical condition in hospital following a five-vehicle collision on the A1.
Police were called at about 6.45pm on Monday to reports of the collision between the slip road joining the A1 from Eaton Socon and the turn-off for the A428.
A spokesman for the constabulary said: "One person has been taken to Addenbrooke's Hospital in Cambridge with life-threatening injuries, and two people have been taken to Hinchingbrooke Hospital in Huntingdon with minor injuries.
"Officers would like to thank members of the public who were caught up in the tailbacks for their patience and support while emergency services dealt with this incident."
The southbound carriageway of the A1 between St Neots and Wyboston was closed overnight while investigations into the incident took place, before re-opening to traffic again at about 7.45am on Tuesday.
Anyone who witnessed the collision, or has dash-cam footage, is asked to contact the Road Policing Unit by calling 101 and quoting CC-09122019-0366.