Published: 16:04, 12 September 2019
| Updated: 19:50, 12 September 2019
The air ambulance landed on the M26 after a crash between a lorry and a motorbike.
Police shut the carriageway in both directions between junction 1 for Sevenoaks and the A21 and junction 2 for Wrotham Heath.
The westbound carriageway reopened before 7pm, but delays were expected to last up to three hours.
Drivers looking to join the M20 and Maidstone area are advised to continue on the M25 to junction 3 for the Swanley Interchange, and take the fourth exit to travel south on the M20.
The Kent bound carriageway reopened at around 7.45pm but there were still long queues.
A police spokeswoman said: "Officers were called at 2.56pm on Thursday, September 12 to reports of a single vehicle collision involving a motorbike at junction 1 of the coastbound M26.
"Both carriageways of the motorway were closed to allow the air ambulance to safely land.
"The rider of the bike is described as having life-threatening injuries. Officers are at the scene."