The walkout by pilots at Lufthansa's core brand, as well as Lufthansa Cargo and Lufthansa CityLine, began shortly after midnight on Monday and will last for 48 hours.

At holiday airline Eurowings, all departures from German airports will be affected on Monday only.

Hundreds of flights are set to be cancelled on Monday and Tuesday, with Lufthansa's hubs in Frankfurt and Munich hardest hit.

The strike marks the fourth wave of industrial action at the group this year. Last week, a one-day cabin crew walkout forced hundreds of cancellations at Germany's largest airline.

The pilots' strike, organized by the Vereinigung Cockpit union, centres on pay disputes, including the company pension scheme and remuneration at the regional subsidiary CityLine.

Lufthansa criticised the union's strike notice, saying it represented a new level of escalation while stressing that it would not shift its position.

Each day of industrial action weakens the airline, said Lufthansa executive board member Michael Niggemann on Monday morning.

He warned that the core Lufthansa Classic airline is already no longer competitive on many routes, meaning that costs cannot be raised further.

"This is about the future viability of Classic," said Niggemann, who also serves as labour director.

Lufthansa will continue to stick to its strategy and only deploy aircraft on routes that are profitable, meaning subsidiaries outside the core brand are set to grow, according to Niggemann.

"These strikes will not affect our strategy," he added.

Despite the industrial actions, around half of Lufthansa's planned long-haul flights are scheduled to lift off on Monday, alongside about a third of medium- and short-haul flights, Niggemann said.

About three out of four flights operated by other Lufthansa-owned carriers including SWISS and Brussels Airlines are expected to be on schedule, he added.

Flights to selected Middle Eastern destinations have been excluded from the strike action.