Three incidents – including a crash which led to a woman being taken to hospital after a two-car crash on the A2 – are causing miles of queues.
Traffic is queuing between the A227 and start of the M2, according to Highways England.
Queues are expected to remain until 1pm while the crash is cleared.
Police spokesman Martin Very said: “Kent Police was called at around 10.35am on June 1 regarding a collision involving two cars on the coastbound carriageway of the A2 near Gravesend.
“Patrols and South East Coast Ambulance Service attended and a woman who reported an injury was taken to a local hospital for medical attention.
“Highways officers remain at the scene arranging vehicle recovery.”
The woman’s injury is not said to be serious or life-threatening and recovery work is ongoing.
Meanwhile, traffic in the opposite direction of the A2 towards London is moving slowly following an earlier incident at the Dartford Crossing, which saw a lorry block the western tunnel.
A spokesman for Highways England said: “The tunnel had to be shut for the lorry to reverse out at 10.45am, with the tunnel closed for around 20 minutes.
“Once the lorry was out, it went down the other tunnel and everything was back to normal.”
But jams have been building between the A2260 junction near Bean and the A296 at Bluewater as a result.
On the M25 anti-clockwise there are queues between Swanley and the Lakeside junction in Essex.
Traffic is expected to take about half an hour to clear the area.
In a separate incident, a broken down vehicle in the outside lane of the M25 at the Darenth Interchange is also adding to heavy traffic.
All lanes are now reopen.