Frankfurt airport, Germany's busiest, was forced Thursday to suspend arrivals and departures after environmental activists forced their way into the apron.

"We are doing everything to remove the climate activists from the tarmac," a police spokesman told AFP.

Frankfurt airport advised passengers to check the status of their flights on its website.

According to climate activist group Letzte Generation (Last Generation), six of its members had used pincers to cut openings in the wire fence before making their way "by foot, with bicycles and skateboards to different points around the runways".

A photo circulated by the group depicted a protester sitting on the tarmac with a banner "oil kills".

The group is pushing for a binding international accord that would lead to an end in oil, gas and coal use by 2030.

Thursday's protest action came a day after similar operations across several European airports.

Activists from Letzte Generation briefly disrupted traffic at Cologne-Bonn airport on Wednesday, while several climate protesters were arrested at London's Heathrow airport.

The protest organisers are part of the A22 Network of groups committed to non-violent climate protests, which said it was planning to disrupt airports in several countries in the coming months.

Protests were planned in Britain, Austria, the Netherlands, Switzerland, Canada, United States and Norway, UK-based activists from the alliance told AFP earlier in July.

Global aviation is responsible for around 2.5 percent of global carbon emissions, more than the annual carbon footprint of Brazil and France combined.