Police have arrested 57 people after climate change activists broke into a secure area of Stansted Airport.
A spokeswoman said 50 had been accused of aggravated trespass, three had been accused of attempting to gain access to a restricted area, and four had been accused of conspiracy to commit a public nuisance.
Protest group Plane Stupid said that, at 3.15am, more than 50 of its campaigners occupied a runway which had been closed for maintenance work.
Stansted said later that 56 inward and outbound flights had been cancelled. A spokesman said all of them were Ryanair flights.
Scores of passengers were leaving Stansted, either to return home or to find hotels after being told that flights were cancelled. The terminal was clogged with thousands of people trying to get information about likely delays.
The protest is over the Government's decision to allow the expansion of the airport with a second runway.
Plane Stupid said aviation was the fastest growing source of emissions and already contributed to at least 13% of the UK's carbon budget.
It also pointed to plans for a new runway at Heathrow.
In a statement, the group said the disruption to flights will prevent "the release of thousands of tonnes of greenhouse gas emissions into the atmosphere".
The GMB trade union, which represents workers at Stansted, revealed that it had been pressing the airport authorities to review security because of concerns over the state of the fencing. It said it was now more important than ever to make sure security was tight at all airports in the UK.
