Traffic is queuing for six miles after a crash involving a lorry near the QEII Bridge.
Three out of four lanes are closed just after the crossing between Junction 1A for the A206 and Junction 1B for Dartford.
Drivers heading into Kent from Essex are being warned to expect delays as congestion is backed up to Junction 31 on the M25 for Grays.
National Highways say it is taking up to an hour-and-a-half to get through.
It is understood the accident happened just before 4pm.
Police and fire crews are at the scene.
