Delays and cancellations are besetting Stansted airport today after dozens of climate change protestors gained access to a secure area of the runway.
Activists from the Plane Stupid group chained themselves to their own security fence at 03:15 GMT this morning.
Essex police have arrested 57 people after cutting the protestors from the fence and the runway was re-opened at 08:10 GMT.
The police said the suspects would be taken to stations and questioned following the incident.
Plane Stupid said it was protesting against government plans to expand Stansted and the environmental impact it would cause.
One protestor, 21-year-old Lily, told inthenews.co.uk: "We're here because our parents' generation has failed us and it's now down to young people to stop climate change by whatever peaceful means we have left.
"We're afraid of what the police might do to us, we're afraid of going to jail but nothing scares us as much as the threat of runaway climate change. We've thought through the consequences of what we're doing here but we're determined to stop as many tonnes of CO2 as we can."
Ryanair has cancelled 56 flights and told passengers to re-book. Airpoprt operator BAA said the demonstration was illegal and "unacceptable".
In a statement on the group's website, Plane Stupid said: "The group intends to maintain its blockade for as long as possible, preventing the release of thousands of tonnes of greenhouse gas emissions into the atmosphere."
The group hopes to prevent departures from the airport, with a hope of slowing the "monumental" impact of climate change.
A spokesperson for airport operator BAA said: "We are happy to engage in serious debates on airport expansion, and we respect people's right to protest within the bounds of the law.
"However, any unlawful or irresponsible behaviour aimed at disrupting the smooth operation of the airport is unacceptable. People should engage in the relevant independent planning inquiries in an open, honest and safe way.
"We will of course investigate this incident and where there are lessons to learn we will do so."
BAA has recently been given permission to expand operations at Stansted.
Green party leader Caroline Lucas said the protest was the result of government confusion.
"As long as the government continues to peddle its hypocritical rhetoric on reducing greenhouse gases, then ploughs ahead with plans to expand Stansted and other UK airports, we will see more protests like the one today.," she said.
Plans are now being finalised to increase passenger numbers from 25 million to 35 million a year at Stansted, with the number of flights leaving the airport increasing from 241,000 to 264,000 a year.
BAA urged passengers to check with their airlines before travelling and warned of cancellations and delays.