Demonstrators protesting against Dakota Access Pipeline say they are trapped on a bridge as North Dakota police fire tear gas, water cannon and concussion grenades at them, according to live reports on social media.

The demonstration is taking place on Highway 1806, just north of the main protest camp against the pipeline.

Officers have also repeatedly deployed water cannon on the protesters in below-freezing temperatures, and are using LRAD sound devices. Earlier, there were reports of rubber bullets fired. Vehicles which appear to be armored humvees have arrived at the scene.

A livestream of the incident has been posted to Facebook Live by Kevin Gilbertt, who claims protesters are trapped on a bridge and being forced to endure tear gas.

“The options are endure the tear gas or trample each other,” Gilbertt says, adding that other protesters are bringing blankets to those trapped on the bridge.