A blue Citroen C3 and a black Vauxhall Astra have crashed in Hitchin, after a driver suffered a medical episode at the wheel.
The incident took place at around 6.40pm on Thursday (October 6), on Walsworth Road, near the junction with Radcliffe Road.
Teams from Hertfordshire police and the East of England Ambulance Service attended the scene.
The driver of the Citroen was taken to hospital in a "serious condition".
Sergeant Tim Davies said: "This incident took place on a busy road near the railway station, I am appealing to anyone who witnessed the collision or has dash cam footage of it to get it touch as this would assist our investigation into what happened.
“Anyone with information is asked to please contact me directly by email via timothy.davies@herts.police.uk.”
Information can also be reported via the Herts police website (www.herts.police.uk/report) or by calling 101.
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