The forecourt of a Tesco filling station in Dorset has been dug up after drivers reported engine problems after buying diesel.
Local press reported that up to 100 vehicles broke down shortly after filling up at the site in Branksome, Poole.
It has now been closed and an excavator was seen at the forecourt but Tesco would not give further details about the work taking place.
A Tesco spokesperson said: "We know customers want to understand how the contamination happened and we are conducting an urgent investigation. This involves complex testing and we want to take the time to make sure we know exactly what happened."