A 10-mile section of a busy motorway has been closed in both directions after a 15ft-deep hole appeared in the central reservation.
Long tailbacks built up after the M2 in north Kent was shut between junction 5 near Sittingbourne and junction 6 south of Faversham.
The Highways Agency said the hole measured around 16ft (5m) by 6ft (2m) and was 15ft (4.5m) deep.
A spokeswoman said: "The road has been closed while urgent safety checks are made following a large hole opening up in the central reservation.
"Agency staff and contractors are working hard to inspect the hole and make the necessary repairs and lanes will be reopened when it is safe to do so."
She added that there were delays both east and westbound in the area of the closure and urged drivers heading to and from the port of Dover to use the M20 instead.
Motoring organisations have warned about the danger of potholes this winter while the Local Government Association has also highlighted the problem and has expressed concern at funding levels for councils.
A Highways Agency spokesman said: "As part of the investigation we will be trying to understand exactly what happened to create the hole."
Earlier this month a sinkhole measuring 30ft (9m) deep swallowed up a car after opening up on the driveway of a house in High Wycombe.Nobody was inside the VW Lupo when the ground on Main Road in Walter's Ash gave way. Firefighters said the hole was about 15ft (4.5m) diameter.
AA president Edmund King said: "Thankfully this was on the central reservation. If a hole of this nature had opened up on a carriageway it could well have led to tragedy."
He went on: "I don't think this is anything to do with potholes or general maintenance. There seems to have been some structural anomaly - perhaps some sort of geological fault or an old mineshaft.
"Clearly, it's a concern that this has happened on a busy motorway that leads to and from the coast. Engineers will want to deal with this as soon as possible. If the stretch of motorway stays shut it will cause traffic problems, but safety must come first."
Mr King said that the Highways Agency, which is responsible for England's motorways and major A roads, has generally got a good maintenance record, with the pothole problem being confined mainly to local authority-run minor roads.
AA roads policy head Paul Watters added: "The M2 started operating in 1965 and I am not aware of any previous collapses so perhaps this is yet another casualty of the exceptionally wet weather.
"We hope the Highways Agency can quickly resolve the problem as this is a key route to the port of Dover and to east Kent."
The Highways Agency said signed diversion routes were in operation for drivers affected by the M2 closure.
These were the instructions: Eastbound traffic should exit the M2 at J5 and follow the "solid black circle symbol" using the A249 south to the M20 (J7). Join the M20 east and exit at J8. Take the A20 east to Charing and join the A252 north. At Challock take the A251 north to rejoin the M2 at J6.
Westbound traffic should exit the M2 at J6 and follow "solid black square" symbol using the above route in reverse to rejoin at J5.
Eastbound traffic wishing to travel to the port of Dover is advised to use the M20 and A20.