Frankfurt Airport, Germany's busiest, was forced to suspend flights after climate activists stormed inside, AFP reported.
"We are doing everything we can to remove the activists from the tarmac," a police spokesman said. Two hours later, travel resumed.
Frankfurt Airport advised passengers to check the status of their flights on its website.
According to the climate activist group Letzte Generation (Last Generation), six of its members used pliers to make an opening in the fence before moving "on foot, with bikes and skateboards to various points around the tracks".
A photo shared by the activists shows a protester sitting on the tarmac with a "petroleum kills" poster.
The group is pushing for a binding international agreement to end the use of oil, gas and coal by 2030.
The protest action took place a day after similar operations at several European airports.
Letzte Generation activists briefly disrupted traffic at Cologne-Bonn Airport on July 24. Several climate protesters were arrested at Heathrow Airport in London.
The organizers of the protest are part of the A22 network of groups engaged in climate protests. They said they plan to disrupt operations at airports in several countries in the coming months.
UK-based campaigners from the alliance announced earlier in July that protests were planned in Britain, Austria, the Netherlands, Switzerland, Canada, the US and Norway.
Global aviation is responsible for about 2.5% of global carbon emissions. | BGNES
