PARIS — A strike by French air traffic controllers seeking better working conditions brought chaos at the height of Europe’s summer travel season after around 40% of flights to and from Paris were canceled Friday.

Disruptions started hitting airports across France on Thursday. These intensified Friday as the national civil aviation authority asked airlines to cancel 40% of flights at Charles de Gaulle, Orly and Beauvais airports serving Paris, half of flights in Nice and 30% of flights in Marseille, Lyon and some other cities.

Despite the preventive cancelations, the authority warned in a statement that “disruptions and long delays are to be expected at all French airports.”

Paris airports’ departure boards were showing a long list of flight delays and cancellations for destinations across France, Europe, North Africa and beyond.

Ryanair was among the airlines that announced widespread disruptions, saying in a statement that it had canceled more than 400 flights affecting 70,000 passengers. The company said the strike affects all its flights over French airspace.

— The Associated Press