Officials have blocked supplies reaching oil pipeline protesters in North Dakota.

Demonstrators have been voicing their concerns over plans to route a $3.8 billion Dakota Access Pipeline beneath a lake near the Standing Rock Sioux reservation and claim the proposals pose a threat to water resources and Native American sites.

State officials have threatened to use fines and a physical blockade to keep protesters from receiving portable bathrooms, food and building materials.

Maxine Herr, a spokeswoman for the Morton County Sheriff's Department, said the primary concern was public safety.

"The governor is more interested in public safety than setting up a road block and turning people away," Ms Herr said.

Officers said they will stop vehicles they believe are headed to the camp and inform drivers they could be fined up to $1,000.

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 activists, who have been protesting for months, said state officials were “bullying” demonstrators and questioned the legality of the fines.

"It's bogus and I don't know about the legality of it," said Kandi Mossett, an organiser for Indigenous Environmental Network.

"We're not afraid. We're moving in and out of the camp at will. So people shouldn't be afraid of coming and supporting the water protectors. They've been bullying us since day one."