Motorists on the M25 motorway faced major delays after the Dartford crossing was shut when a lorry caught fire.
Kent Police said the Queen Elizabeth II bridge was closed for more than three hours on Friday to allow the Highways Agency to deal with the incident.
The Dartford tunnel was used for both north and southbound traffic following the fire at about 1220 BST.
Cars were left queuing from junction 4 of the anti-clockwise carriageway.
There were also tailbacks up to junction 25, near Enfield, and delays on surrounding roads in east London and west Essex.
'Exceptionally long queues'
A Highways Agency spokesperson said: "As a result of an emergency situation on the Dartford-Thurrock river crossing, the QE2 bridge has been closed for a significant period of time and the Highways Agency has temporarily suspended all charges on the crossing until further notice.
"The decision was made at 3.45pm this afternoon to help ease the exceptionally long queues which have built up as a result of the emergency and also to reduce the risk of minor collisions in queuing traffic.
"We are doing all we possibly can on what is routinely a very busy period at the crossing."