Drivers are being delayed by two hours as a major road bridge linking Essex and Kent remains closed after a pair of Just Stop Oil protesters climbed up the structure.

Essex Police said officers were called shortly before 3.50am on Monday to a report that two people had climbed on to the Queen Elizabeth II Bridge at the Dartford Crossing.

Just Stop Oil said in a statement that two supporters of the group had scaled the structure “to demand that the Government halts all new oil and gas licences and consents”.

National Highways said the incident was causing delays of two hours, with six miles of congestion on the anti-clockwise carriageway and five miles in the opposite direction.

An Essex Police spokesman said: “The QEII bridge is closed to allow us to resolve the situation as safely as possible and a diversion is in place through the tunnel.

“This is a complex operation due to the height at which the protesters are currently situated and it may take some but we are working as quickly as possible.”

The spokesman said the force’s “priority” is to “keep people safe and keep Essex moving”.

He added: “We will take action against anyone who puts life in danger or thinks they can selfishly stop others getting to work or getting on with their lives.

“We appreciate your patience and understanding and will keep you updated through the day.”

Just Stop Oil said that “two climbers ascended the two 84m masts on the north side of the Queen Elizabeth II Bridge, forcing the police to stop traffic from entering the bridge”, adding “it is expected that the bridge will remain shut for at least 24 hours”.

Morgan Trowland, 39, a bridge design engineer from London, said in a statement released by Just Stop Oil: “As a professional civil engineer, each year as I renew my registration I commit to acting within our code of ethics, which requires me to safeguard human life and welfare and the environment.

“Our Government has enacted suicidal laws to accelerate oil production: killing human life and destroying our environment.

“I can’t challenge this madness in my desk job, designing bridges, so I’m taking direct action, occupying the QEII bridge until the Government stops all new oil.”

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

The A282 Dartford Crossing is currently the only way to cross the Thames east of London by road.

The 1.7-mile (2.8km) long QEII Bridge southbound and two 0.8-mile (1.4km) long tunnels northbound link Essex and Kent.

The A282 also connects directly at both ends with the M25 London orbital motorway, one of the busiest motorways in Europe.