A coach has overturned on the M25, with firefighters working to free two people trapped in the vehicle.
Lanes one and two have been closed, as has the exit slip road at J3, Kent Highways said.
Police, ambulance and fire services were called to the scene at the M25 at Swanley on the anti-clockwise carriageway just before 4pm.
No casualties have been confirmed.
The Princess Royal University Hospital in Orpington, Kent, is on major incident alert, a spokesman said.
No patients have yet been received and the hospital is on standby, he added.
A statement from Kent Police said: “Kent Police was called at approximately 4pm on Monday August 13 to reports of a collision involving a coach on the anti-clockwise carriageway of the M25 near to junction three.
“Officers are currently at the scene with South East Coast Ambulance Service and Kent Fire and Rescue Service.
“The junction three slip road on the anti-clockwise carriageway and lanes one and two are currently closed.
“There are delays to traffic and motorists are advised to seek alternative routes where possible.”
Three fire engines and “several vehicles from the heavy rescue team” were sent out “as a precaution”, the Kent Fire and Rescue spokesman said.
Police are urging motorists to plan ahead due to delays.