Police were on the scene at a hole in the road in Welwyn Garden City.
A motorist discovered the hole at 10.49am today, at Mundells roundabout, and phoned the police.
Police put cones around the area.
A Hertfordshire County Council spokeswoman said: “We have had reports of a hole in the road.
“Our highways contractor Ringway is currently investigating. We do not know what caused it but they are down there looking into it.
“We will take any action to make sure the area is safe.”
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