Climate activists protesting against the use of fossil fuels like kerosene disrupted operations at the airports in Hamburg and Dusseldorf on Thursday morning, causing chaos just as school vacation get underway in Germany. 

Videos posted by members of the “Last Generation” group showed activists blocking the runway in Hamburg as well as airfield taxi ways in Dusseldorf since about 6 am local time, forcing a temporary halt to operations. Police are on site, and Hamburg suspended takeoffs and landings.

German school summer vacation started on Wednesday in some parts of the country, kicking off the high season for air travel in Europe’s largest economy. The protest disruptions add to uneven operations at airports amid strikes and a lack of personnel in areas like baggage handling.

Airports have become targets of climate activists who seek to highlight the aviation industry’s contribution to global warning. Berlin’s airport security perimeter was compromised late last year when protesters cut their way through the main fence and gained access to the runway. 

Hamburg and Dusseldorf are among the country’s largest airports, serving both short and long-haul routes. Emirates, the world’s biggest international airline, serves both cities. 

The Last Generation group argues that governments, businesses and citizens aren’t doing enough to cut greenhouse gas emissions. The aviation industry has pledged to become carbon neutral by 2050.