Germany’s busiest airport cancelled a total of 270 flights after environmental activists launched a co-ordinated effort to disrupt air travel across Europe at the height of the summer holiday season.

Frankfurt Airport said flights were halted for safety reasons after climate activists breached security fences, triggering a response from police, firefighters and airport security officers.

Its runways were back in operation by 7.50am local time.

By Thursday evening, airport operator Fraport said 270 flights had been cancelled out of 1,400 scheduled for the day, German news agency dpa reported.

Equipment left behind after a hole was cut in a fence
Equipment left behind after a hole was cut in a fence (Michael Probst/AP)

“We sharply condemn these unauthorised demonstrations, and we reserve the right to take legal action against the participants,” the airport said.

“Their activities pose severe danger to flight operations – possibly putting human life at risk.”

Environmental groups said they planned to target airports around Europe this summer to remind people about the link between fossil fuels, such as those used by airliners, and climate change.

The groups are calling for governments around the world to end the extraction and burning of fossil fuels by 2030.

The Last Generation group, which organised the Frankfurt demonstration, said six protesters cut holes in the perimeter fence and headed towards the runways on foot, bicycles and skateboards.

It was the second time in as many days that a protest by Last Generation caused disruption at a German airport.

On Wednesday, five protesters glued themselves to a taxiway at Cologne-Bonn Airport, forcing a roughly three-hour halt to flights. That protest resulted in 31 flights being cancelled.

Police officers study the hole in the fence
Police officers study the hole in the fence (Michael Probst/AP)

Climate activists staged similar action in Finland, Norway, Switzerland and Spain on Wednesday.

At Helsinki Airport, a handful of protesters blocked the main check-in area for about 30 minutes, but police said it caused no delays to flights or other disruption.

At Oslo’s main Gardermoen airport, three activists entered the runway area, waving banners and disrupting air traffic for about half an hour. Police said there were no major flight delays.

Police in London said on Wednesday that they had prevented a planned protest at Heathrow Airport that could have had a significant impact on Europe’s largest airport. Seven members of the group known as Just Stop Oil were arrested at Heathrow and three others were taken into custody at other locations as part of an “intelligence-led” operation, the Metropolitan Police said.

Last week, the German cabinet approved legislation that would impose tougher penalties on people who break through airport perimeters.

The bill, which still requires approval by legislators, proposes punishment ranging up to a two-year prison sentence for people who intentionally intrude on airside areas of airports such as taxiways or runways, endanger civil aviation, or enable someone else to.