Lufthansa pilots are set to extend their strike to two-days causing potential disruption to thousands of passengers.
Today’s strike has affected short and long-haul flights and Thursday’s action will only hit long-haul services.
Lufthansa has already cancelled 750 flights, affecting 80,000 passengers.
The industrial action, protesting pilots' early retirement scheme, had been scheduled to last for 24 hours.
It is currently affecting Lufthansa flights throughout Germany. Services with the airline's Eurowings and Germanwings subsidiaries are running as normal.
Bettina Volkens, Lufthansa's director of industrial relations, called today's strike "completely disproportionate".
The strike is the latest in a series of walkouts called by the Vereinigung Cockpit union, which is protesting plans to change the current scheme that sees pilots retire at 55 and retain some of their pay until they reach the state pension age.
Lufthansa said it has made concessions in recent talks, including giving the pilots a 5 per cent pay rise.
The frequent strikes by Lufthansa — and Air France — pilots are the result of the long-established carriers clashing with unions as they try to cut costs to compete with budget airlines.
Earlier this month, Lufthansa said it lost €232 million last year due to ten such strikes.