German airline Lufthansa cancelled around 750 short- and medium-haul flights Wednesday, hitting tens of thousands of passengers, as pilots staged fresh strike action in a bitter dispute over early retirement.
Just over half of the carrier's scheduled 1,400 domestic and European flights to and from Frankfurt and Munich were grounded, affecting around 80,000 passengers, a Lufthansa spokesman said.
The strike was set to continue throughout Thursday when it will shift to target long-haul and cargo services.
The two-day walkout is the 12th bout of strike action to hit the German airline since last April over management plans to change the pilots' transitional pension arrangements.
Flights operated by Lufthansa's subsidiaries Germanwings, Eurowings, Swiss and Austrian Airlines were not affected.
A Lufthansa spokesman said the airline had sought to warn passengers of Wednesday's strike ahead of time via text messages sent by mobile phone and email.
At Munich and Frankfurt airports, there were no reports of large groups of stranded passengers Wednesday, national DPA news agency said.
Pilots' union Vereinigung Cockpit (VC) announced late on the eve of the walkout that the initially planned one-day stoppage would be extended by another day.
Lufthansa slammed the latest action as "incomprehensible" and said that it expected 42 of its 85 flights scheduled to leave Germany Thursday to be scrapped but that no cargo services were set to be cancelled.  
Long-haul services are expected to resume as far as possible on Friday, the airline said, adding that, similarly, short- and medium-haul traffic was set to be back to normal from Thursday.
The company said it had called on other airlines within the Lufthansa group to help to cover routes.
- Keep talking -
The dispute hinges on plans by Lufthansa to scrap an arrangement under which pilots can retire at 55 and receive up to 60 percent of their pay until they reach the statutory retirement age of 65.
Pilots are also concerned over Lufthansa's aim to further develop its low-cost activities as it faces growing competition.
Lufthansa said in a statement late Tuesday that calling Wednesday's strike lacked "any proportionality", and that the extension was "completely incomprehensible".
It had made an improved offer to the pilots' union in recent days, Lufthansa said, calling on VC to immediately continue talks.
"Instead of working on sound solutions for the future, the VC is inflicting damage now on Lufthansa customers worldwide," it fumed in a statement.
It also said it was "irresponsible" to refuse any form of negotiation over "privileges" for around 5,400 of the company's 12,000 workers.
For its part, Vereinigung Cockpit accused Lufthansa of not having "moved a millimetre" despite its claims, and urged the airline's bosses to negotiate "seriously" or accept "an overall settlement".
In the previous round of strike action in mid-February, Lufthansa's low-cost subsidiary Germanwings was forced to scrap close to 340 outbound flights from Germany.
Overall in 2014, the repeated strikes cost Lufthansa an estimated 232 million euros ($245 million).
Last week the airline said it expected to see a "tangible" improvement in its underlying earnings this year after profits nosedived in 2014.
Lufthansa's profits were hit by a range of factors last year, including changes in the value of a convertible bond it had issued in 2012, and losses on its options for fuel price hedging.
Strike action by its pilots also weighed on earnings.