Seventeen people have been arrested after a protest at Stansted Airport in Essex temporarily halted take-offs and landings on Tuesday.
Police were called at 21:30 BST as a group entered a non-commercial runway and locked themselves in an aircraft.
Those involved were trying to stop a charter flight which they claim was due to deport people to Nigeria and Ghana.
A spokesman for the airport said the runway was closed as a "precaution" but reopened at 23.17 BST.
In total, 23 incoming flights were diverted to other airports, including scheduled arrivals from Naples, Cologne, Glasgow, Riga, Belfast and Bilbao.
The spokesman said the protest took place in a remote part of the airport used by private operators, away from the passenger terminal or runway.
Essex Police said on Wednesday that officers were at the scene and in the process of removing protesters from the aircraft, which was destined for Nigeria.
Acting Assistant Chief Constable Sean O'Callaghan said police "quickly contained" the protesters in one area of the airport.
"We continue to work closely with our partners and the airport authority as we are working to apprehend the protesters quickly and effectively," he said.
He added that there was "minimal impact" on the airport. The force said three arrests had been made so far, but no more details were given.
The activists posted images of the protest on social media, including a photograph of people lying on the ground as they were surrounded by security staff and police.
In a Facebook post they said the flight was due to "forcibly deport dozens of people to Nigeria and Ghana" but this has not been confirmed.
One of the protestors, Susan James, said: "I don't want to stay silent in the face of mass deportations that are deliberately rushed and secretive."