Heathrow Airport was forced to shut down operations at its northern runway for three hours after members of the campaigner group Plane Stupid occupied the area in protest against the proposed expansion.
The group has been protesting against the Airports Commission's recommendation on the construction of a third runway at the airport.
According to Plane Stupid, the new runway would result in the country failing to meet with the climate change targets as it is expected to lead to an increase in noise and air pollution.
The airport said in a statement that while the southern runway remained open through the incident, the protest might lead to delays and cancellations.
An airport spokesperson was quoted by The Guardian as saying: "A group of people have breached the airport perimeter fence and are currently staging a protest on the northern runway.
"We are working closely with the police who are dealing with the incident. The southern runway remains open.
"Our priority remains to ensure the safety of the airport community, including passengers, employees and protesters."
The protests have led to cancellation of at least seven British Airways domestic and short-haul flights from Terminal Five, including one to Dublin, Sky News reported.
So far, the police have arrested six of the total 13 activists on suspicion of Aviation Act offences.
The group claims that the new runway will only benefit 15% of the county's population who take 70% of the country's flights.
Image: Members of Plane Stupid have been protesting against the construction of a third runway at the Heathrow airport. Photo: courtesy of Plane Stupid.