Five climate change protesters have been arrested on suspicion of aggravated trespass at the site of a gas-fired power station.
Nottinghamshire Police said some of those involved in the protest had scaled buildings at West Burton Power Station after gaining access to the site at about 1.20am today.
A police spokesman said: "Around ten (protesters) are thought to have climbed the water towers and have secured themselves to restrict their removal.
"Searches are ongoing to find a number of other people who are also believed to have gained access to the site."
One of the protesters told the Press Association a total of 17 people had climbed two towers roughly 80 metres apart.
Speaking by mobile phone from the site, the woman, who gave her name as Ewa, confirmed the group was demonstrating against climate change and fuel poverty, as well as to highlight the need for renewable energy rather than "expensive and dirty" gas.
Ewa said: "Our motivation for this protest is to try and stop this government from locking us into a dependency on gas for the next 30 years.
"If billions can be found to bail out corrupt banks then billions can be found to fund a renewable energy economy."
Such an economy would create hundreds of thousands of "green" jobs, reduce household energy bills and benefit the environment, according to the protest group, who say they have sufficient supplies to stay at the power station for around a week.
Ewa added: "It's unusual that we are linking this directly to fuel poverty.
"We shouldn't be investing in any gas whatsoever."
A worker at the site, who did not want to be named, said all but essential staff had been sent home for the day.
He said: "They're still building the gas site. It's nearly up and running. It's being tested."
Steve Pryle, from the GMB union, said: "All our members have been sent home.
"We were told approximately 200 of our members have been sent home."
He said he had been told there were 26 protesters on site.
"What we want to know is how on earth these guys got on site.
"It's a secure site and there is supposed to be tight security to protect the site against attacks and terrorism."
The "no dash for gas" campaigners are protesting against moves to build new gas-fired power stations such as West Burton, warning it would leave the UK dependent on a polluting and increasingly expensive fossil fuel for decades.
The Government has backed the development of up to 20 gas-fired power stations as part of its strategy for future energy supplies.
Ministers insist that continuing use of gas without technology to trap and permanently store carbon emissions is compatible with targets to cut greenhouse gases to tackle climate change.
But Friends of the Earth's head of campaigns, Andrew Pendleton, said: "This morning's protest sends a powerful message that a new dash for gas is wrong - gas is the main reason our fuel bills have been rocketing, and staying hooked on it will cost us a fortune.
"The Government talks the talk on a greener economy, but its plans for 20GW of new gas plants far exceeds what's needed as we switch to renewable energy, and could easily bust our targets for tackling climate change.
"Rather than tying us into decades of dirty and increasingly costly gas, the Coalition should be making clean British energy and energy saving the powerhouse of our economy - creating hundreds of thousands of new jobs."
A spokeswoman for EDF confirmed that only essential staff were leaving and entering the site while the protest continued.
In a statement she said: "The station is in a commissioning phase at the moment and the first unit is expected to be fully operational by the end of the year.
"While the protest is ongoing, only essential staff are leaving and entering the plant."
She said the protest would not affect supplies to energy users in the area or to the national grid.
"Generation at the adjacent coal station is unaffected," she added.
In a statement, EDF said: "We support the right to peaceful protest. However, any unlawful action is of serious concern and puts at risk the safety of the individuals involved.
"Our site management and security teams have taken the appropriate action in protecting the safety of the public, personnel and plant.
"EDF Energy is committed to a low-carbon future through new generation and increased energy efficiency.
"As part of our sustainability commitments, we aim to reduce the carbon intensity of our generation by 60% by 2020 from a 2006 base.
"Alongside our new gas plant at West Burton, new nuclear and renewables are major elements in our future generation plans.
"EDF Energy is also the country's largest generator of low- carbon electricity through its existing nuclear and renewables fleet."