Hundreds of protesters have been taking part in a march against coal-fired power plants near Kingsnorth power station
Four protesters have been arrested after breaching a perimeter fence surrounding Kingsnorth power station.
Police said the activists were stopped before they reached the inner fence. Four people were also arrested trying to launch a boat on the River Medway.
Officers in riot gear and about 15 police vans were stationed in front of the power station on the Hoo peninsula.
About 100 activists opposing the firm's plans to build new coal-fired units in Kent had marched to the plant gates.
They had said they wanted to shut it down as part of a day of action against climate change.
E.on spokesman Jonathan Smith denied activists claims that the power station had stopped running.
He said: "It is operating, it's business as usual. There is always a lower demand for power on a Saturday, but it is running."
About 1,500 people have been stationed at the Climate Camp, which is one mile from Kingsnorth, over the past week.
Campaigners carrying drums and banners, and flanked by police officers, marched from the site to the gates of the power station on Saturday morning.
They listened to speeches by environmental campaigners such as Liberal Democrat MEP Chris Davies once they were outside the plant.
Most of the protesters returned to the camp in the afternoon apart from about 20 who created a human chain in front of the site's gates and had to be removed by police in riot gear.
Police have stopped people taking part in the "Great Rebel Raft Regatta"
The procession was part of the activists' "four-pronged attack" on Kingsnorth.
Four demonstrators trying to launch a boat on to the River Medway as part of a "Great Rebel Raft Regatta" were arrested by Kent Police and four boats were stopped.
A spokeswoman for the Climate Camp claimed between 20 to 30 rafts had taken to the River Medway as part of the river protest.
She also said eight kayakers were detained by police when they got close to the station.
The Medway Port Authority harbour master announced on Thursday that he would not give permission to any procession or regatta to take place under river byelaws because of safety concerns.
In July E.On was granted an injunction to prevent campaigners getting access to a jetty on the River Medway where fuel is delivered to the power station.
Campaigners from the Climate Camp said they had also planned to approach the power station by air and through the undergrowth surrounding the site.
E.On plans to build two new cleaner coal units on the site, which it claims will be 20% cleaner.
Medway Council has approved the scheme, which would be the first coal-fired power station to be built in the UK for 24 years, and the final decision will be made by the government.
If approved, E.On said the power station would be operational by 2012 and would provide energy for 1.5 million homes.