Police made a number of arrests today during a second raid at a site where 400 eco-activists are gathering for a week-long environmental protest.
Officers faced resistance as they entered the Camp for Climate Action site near Kingsnorth power station in Kent at around 5.30am to remove vehicles blocking its entrance.
The windows of a van were smashed during the stand-off, protesters said.
A Kent Police spokeswoman said officers had so far made six arrests today in connection with the Climate Camp protest.
Four men aged between 24 and 45 were arrested on suspicion of public order offences between 5.50am and 6.30am, while one man aged 27 was arrested on suspicion of obstructing a police officer.
Another man aged 40 was arrested at 12.30am on suspicion of possessing a prohibited weapon.
A statement by Kent Police said officers had become "increasingly concerned" about the lack of safe access or emergency exit routes from the site in Dux Court Road, near Hoo.
Police said protesters had increased the number of vehicles obstructing the gate after concerns were raised by officers.
Assistant Chef Constable Gary Beautridge said: "We used absolutely the minimum force necessary to ensure safe access and entry routes to and from the site.
"However, the response from protesters, including those who have "locked on" to the vehicles causing the obstruction, has required us to increase our presence on the site."
Terry Graves, a Camp for Climate Action spokesman, said: "The police are claiming the vehicles were blocking the emergency exit and were abandoned, both of which are lies."
He claimed the "heavy handed" police action was designed to dissuade people from coming to the camp.
On Thursday, police seized bolt croppers, super glue, padded suits and climbing ropes during a raid at the site.
Two people, a man and a woman, were arrested for obstruction and were bailed to appear at Medway Magistrates' Court on August 28.
Campaigners are opposed to proposals by the plant's owners, E.On, to build a new on-site coal-fired facility - the first such plant to be built in Britain for more than 30 years.
More than 1,000 protesters are expected to take part in a planned day of direct action on Saturday to "shut down" Kingsnorth.