Around 140 flights at Germany's busiest airport have been cancelled after climate protesters glued themselves to the tarmac.
Activist group Last Generation said six protesters headed towards the runway at Frankfurt Airport wearing fluorescent orange vests and carrying signs that read "Oil kills", after cutting a hole in the perimeter fence.
Their presence triggered a response from police, firefighters and airport security officers, apparently resulting in arrests. Eight people are currently in police custody, according to Last Generation.
All runways were operational again by 7.50am local time (6.50am UK time) but the airport warned passengers that further delays and cancellations are expected later today.
The airport said it "sharply condemns" the protest and "reserves the right to take legal action" adding that the protesters' actions "pose severe danger... putting human life at risk".
The protest is part of environmental activist groups' plans to target airports around Europe this summer, demanding that governments around the world end the extraction and burning of fossil fuels by 2030.
The protest in Germany coincides with the government's decision last week to approve new legislation, which would see tougher penalties imposed on airport trespassers.
Though the bill is still awaiting approval, if implemented, it could see punishments such as a two-year prison sentence for those who intentionally intrude into airside areas.
Germany's home secretary Nancy Faeser, who has pushed for the new legislation, called Thursday's protest "dangerous, dumb and criminal", and said acts like it should be "punished more severely".
Currently, intruders who access airside areas are only fined, though a prison sentence of up to five years is possible in some cases.
