Work on a gas-fired power station has been disrupted after protesters broke into the site and scaled two chimneys.
More than 20 "no dash for gas" campaigners made their way into West Burton Power Station in Nottinghamshire in the early hours of Monday morning, with 16 climbing and securing themselves to two chimneys at the site, according to police.
Five women, from Manchester and Leeds, were arrested as the group made their way into the site at around 1.20am. They are being questioned on suspicion of aggravated trespass, Nottinghamshire Police said.
The 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.
Speaking by mobile phone from the site, one of the protesters, who gave her name as Ewa, said a total of 17 people had climbed two towers roughly 80 metres apart.
She said 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."
The protest has raised concerns over security and the safety of the site and workers.
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."
"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."
EDF confirmed that only essential staff were leaving and entering the plant while the protest was ongoing, with the rest being sent home for the day.
A spokeswoman for the energy firm 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."
Andrew Pendleton, Friends of the Earth's head of campaigns, 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."
Nottinghamshire Police said negotiations are ongoing with campaigners and EDF to bring the protest to a peaceful end.
Assistant Chief Constable Paul Broadbent said: "People have the right to protest, but not when it prevents, or restricts the rights of, others from going about their lawful business.
"There are 101 ways to protest lawfully. Breaking into someone else's property is not one of them.
"Those involved in planning and participating in this illegal action can expect to be arrested."