Meanwhile, North Dakota law enforcement will not make spot checks on vehicles headed to the camp where activists are based, the governor's office said on Wednesday, backing away from a previous plan.

Activists have spent months protesting plans to route the $3.8 billion (£3 billion) Dakota Access Pipeline beneath a lake near the Standing Rock Sioux reservation, saying it poses a threat to water resources and sacred Native-American sites.

The 1,172-mile (1,885 km) pipeline project, owned by Texas-based Energy Transfer Partners LP, is mostly complete, except for a segment planned to run under Lake Oahe, a reservoir formed by a dam on the Missouri River.

“I figured this was more important than anything else I could be doing,” Guy Dull Knife, 69, a Vietnam War Army veteran, told Reuters at the main camp.

Dull Knife, a member of the Oglala Lakota tribe from the Pine Ridge Reservation of South Dakota, said he has been camping at the protest site for months.

Veterans Stand for Standing Rock, a contingent of more than 2,000 US military veterans, intends to go to North Dakota and form a human wall in front of police, protest organisers said on a Facebook page. Organisers could not immediately be reached to comment.

Morton County Sheriff's Office spokesman Rob Keller said in an email his agency was aware of the veterans' plans, but would not comment further on how law enforcement will deal with demonstrators.

Former US Marine Michael A. Wood Jr is leading the effort along with Wesley Clark Jr, a writer whose father is retired US Army General Wesley Clark.

US Representative Tulsi Gabbard, a Democrat from Hawaii and a major in the Hawaii Army National Guard, has said on Twitter she will join the protesters on Sunday.

The veterans will bolster the thousands of people protesting at camps located on US Army Corps of Engineers land, north of the Cannonball River in Cannon Ball, North Dakota.

The Army Corps, citing safety concerns, has ordered the evacuation of the primary protest camp by 5 December, but said it would not forcibly remove people from the land.

Protesters occupy Standing Rock reservation, North Dakota Show all 15 1 /15 Protesters occupy Standing Rock reservation, North Dakota Protesters occupy Standing Rock reservation, North Dakota A person pours a pepper spray antidote into a protester's eyes during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota Reuters Protesters occupy Standing Rock reservation, North Dakota People swim across a river to where the police officers are standing guard during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota Reuters Protesters occupy Standing Rock reservation, North Dakota A man holds up a ceremonial object while police officers look down from a hill during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota, U.S Reuters Protesters occupy Standing Rock reservation, North Dakota People protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota November Reuters Protesters occupy Standing Rock reservation, North Dakota Two people stand in the water of a river while police officers guard the shore during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota Reuters Protesters occupy Standing Rock reservation, North Dakota A man stands on a makeshift bridge over a river while police officers stand on the opposite shore during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota, U.S Reuters Protesters occupy Standing Rock reservation, North Dakota Police use pepper spray against protesters in a boat during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota, U.S Reuters Protesters occupy Standing Rock reservation, North Dakota Police use pepper spray against protesters in a boat during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota, U.S Reuters Protesters occupy Standing Rock reservation, North Dakota Police use pepper spray against protesters in a boat during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota, U.S Reuters Protesters occupy Standing Rock reservation, North Dakota Tonya Stands recovers after being pepper sprayed by police after swimming across a creek with other protesters hoping to build a new camp to block construction of the Dakota Access Pipeline, near Cannon Ball, Reuters Protesters occupy Standing Rock reservation, North Dakota Dakota Access Pipeline protesters stand in the foreground and in the waist-deep water of the Cantapeta Creek, northeast of the Oceti Sakowin Camp, near Cannon Ball, N.D., Wednesday, Nov. 2, 2016. Officers in riot gear clashed again Wednesday with protesters near the Dakota Access pipeline, hitting dozens with pepper spray as they waded through waist-deep water in an attempt to reach property owned by the pipeline's developer. Reuters Protesters occupy Standing Rock reservation, North Dakota Dakota Access Pipeline protesters stand in the foreground and in the waist-deep water of the Cantapeta Creek, northeast of the Oceti Sakowin Camp, near Cannon Ball, N.D., Wednesday, Nov. 2, 2016. Officers in riot gear clashed again Wednesday with protesters near the Dakota Access pipeline, hitting dozens with pepper spray as they waded through waist-deep water in an attempt to reach property owned by the pipeline's developer. Reuters Protesters occupy Standing Rock reservation, North Dakota People who were tear gassed return to the shore during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota, Reuters Protesters occupy Standing Rock reservation, North Dakota People yell at police officers standing on the opposite shore of a river during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota, U.S Reuters Protesters occupy Standing Rock reservation, North Dakota Police use pepper spray against protesters in a boat during a protest against the building of a pipeline on the Standing Rock Indian Reservation near Cannonball, North Dakota, U.S Reuters

The state's latest decision to avoid making spot checks on cars entering the protest site indicates local officials will not actively enforce Monday's emergency order to evacuate the camp issued by Governor Jack Dalrymple, who had cited a coming blizzard.

Local law enforcement said on Tuesday they planned a blockade of the camp, but local and state officials later retreated, saying they would only check vehicles for certain prohibited supplies like propane, and possibly issue fines.

“The governor has said there will be no checkpoints, no stopping of vehicles,” said Jeff Zent, a spokesman for Dalrymple.