The Dartford Crossing bridge has been closed and there are long tailbacks after two oil protesters climbed the structure.

There are two-hour delays in both directions and five to six miles of congestion, said National Highways.

Climate change activist group Just Stop Oil said two of its supporters had scaled the 84m-high masts on the north side of the QE2 bridge "to demand that the government halts all new oil and gas licences and consents".

It's the latest protest by the group's activists, who on Sunday sprayed an Aston Martin showroom with orange paint and a few days earlier threw tomato soup over Van Gogh's Sunflowers. 

"The bridge has been closed while we resolve the incident which we will do as quickly and as safely for all involved," Essex Police said.

"It does mean that we have had to close the bridge to traffic, but a diversion is going to be put in place through the tunnel.

"This is likely to cause delays throughout this morning and this incident may take some time to resolve due to the complexities of safely getting people down from height."

The bridge, which links Essex and Kent, was shut after the report of climbers was received just before 3.50am. As daylight broke, they were pictured dangling from its steel cables.

The Dartford Crossing also includes two tunnels and is notoriously busy, being the only way to cross the Thames east of London by road.

Engineer and protester Morgan Trowland, 39, released a statement through Just Stop Oil.

"I can't challenge this madness in my desk job, designing bridges, so I'm taking direct action, occupying the QE2 bridge until the government stops all new oil," he said.

Another protester, identified only as Marcus, 33, a teacher, said: "Only direct action will now help to reach the social tipping point we so urgently need."

There was anger from drivers who faced long delays trying to get to work.

"I'm currently sitting in traffic burning loads of fuel waiting to get on the Woolwich ferry to cross the Thames to get to work…. No thanks to the two d******** who have climbed the #darfordcrossing," tweeted Nick Reave.

"My husband works for electricity board for London and can't even get out our road," posted Sioxsie Wild.

"He had VITAL engineering job to do. Ambulances are stuck and emergency services are stuck. This is causing more damage and literally harm to life."

Southbound/clockwise traffic is being diverted via the East Bore Tunnel, said National Highways. Traffic northbound/anti-clockwise is being confined to the West Bore Tunnel only.