At least two protesters have managed to get onto the other side of the fence at Hinkley Point. Another was stopped by police as she tried to climb over.
More protesters have turned up with telescopic ladders. Police will not allow them to use them to put up posters.
Protesters have prepared 500 wild flower 'seed bombs' which they are throwing over the fence. They say they want to symbolically reclaim the land for nature.
Green Party leader Natalie Bennett has arrived to support the action of the protesters.
An Avon & Somerset police inspector on site says a number of arrests have been made. He would not confirm the exact number but says it is in single figures.