An accident in one of the northbound Dartford Crossing tunnels led to 10-mile motorway tailbacks.
Traffic queues reached 10 miles at the height of the delays
The west tunnel had to be closed for nine hours on Wednesday after a lorry struck a ventilation fan, causing damage along 300m of the roof.
M25 anti-clockwise traffic from Kent to Essex was diverted through the east tunnel, with queues stretching back from Dartford to junction four.
The tunnel reopened on Wednesday afternoon after the crash at 0600 GMT.
Highways Agency engineers carried out repairs to tiles and panelling inside the west tunnel.
No other vehicles were involved and there were no injuries reported.
Dartford's MP, Dr Howard Stoate, said the crash highlighted the need for another Thames crossing between Essex and Kent.
"You can see from today's chaos that a relatively minor incident causes absolute chaos for tens of thousands of people for nine hours," he said.
"The case now is overwhelming - we have to have another crossing."
He added that traffic was increasing at the crossing by about 3% to 4% each year and in five years' time there would be 20% more traffic.
He said: "Just imagine the chaos that will ensue if we don't do something very urgently indeed."
Latest figures say that 17,000 HGVs use the Dartford Crossing every day, with more than 6,000 vehicles crossing between Kent and Essex each hour.
Two feasibility studies looking at the possibility of another crossing were announced last month.
Kent and Essex county councils and Transport Minister Stephen Ladyman have also said that traffic pressures at the Dartford Crossing will continue to get worse.
Kent County Council has said an extra crossing could be a rail or road link between the A2 in Kent and the A12 in Essex, perhaps crossing the Thames Estuary at Dartford, Gravesend, Sheppey or Grain.