Kate Warren secured herself to the gate with a D-lock at about 6am (AEDT) this morning to protest development of Whitehaven Coal's $767 million Maules Creek open-cut mine at Boggabri.

Protesters have been campaigning at the site since Monday in an attempt to turn back vehicles seeking to clear the forest for construction of rail infrastructure.

It is believed that close to 30 protesters were at the scene this morning, along with nine police officers, who cut Warren free before arresting her and taking her away.

Trucks, including water tankers, had been stopped from entering the mine site.

Protesters say the mine development work, including roads and a rail line, will destroy valuable forest, as well as Aboriginal cultural and burial sites.

The Forestry Corporation of NSW confirmed this week that it had closed the Leard State Forest after concerns from police and the Rural Fire Service about protesters occupying the forest.

The closure has angered protesters, who will now be liable for removal and prosecution and face fines if found in the forest.