A strike by Lufthansa ground and cabin staff over pay has barely disrupted flights to and from German airports, the airline said on Monday, but union officials said the impact would grow in coming days.

Tens of thousands of air passengers had faced travel chaos at the height of the holiday season due to walkouts by more than 4,000 members of the Verdi services union.

The open-ended strike, which officially started at midnight (9 p.m. British time on Sunday) at some of Germany's largest airports, including international hubs Frankfurt and Hamburg, threatened to hit areas from catering and cargo to maintenance and repairs.

"We have had 1,000 flights fly so far today without any major problems - no cancellations and only a few minor delays," a Lufthansa spokesman said at about 1200 GMT.

Television pictures showed planes taking off as usual and departure boards indicating only short delays. Lufthansa said it had limited the impact of the walkouts by taking preventative action, such as reassigning non-striking staff to other tasks.

"Today we have come through relatively well. It is difficult to predict how things will look tomorrow or on other days," the spokesman said.

Some analysts have put the cost of the strike at about 5 million euros (3.9 million pounds) per day for Lufthansa, Europe's second biggest airline by passenger numbers.

Like other airlines, Lufthansa is under pressure to keep costs down due to soaring fuel prices.

At 1220 GMT, shares in the flag carrier were down 2.14 percent and were underperforming the wider DAX index which was down 1.04 percent.

Verdi said the aim of the strike was to hurt the company rather than to cause many cancellations. Local media reported that many passengers had rebooked flights with other airlines rather than risk delays with Lufthansa.

"Our strike is going very well," Verdi negotiator Erhard Ott told ZDF, saying workers in Frankfurt, Munich, Cologne, Hanover and other cities had staged walkouts.

Cargo, maintenance and catering had been hit, he said.

"The emergency plan implemented by the company has cost a lot of money," Ott said, adding that the effects of the strike were likely to grow in coming days.

Verdi, which represents 52,000 air industry workers, wants a 9.8 percent pay rise for one year. Lufthansa is offering 6.7 percent over 21 months and a one-off payment. Some 91 percent of union members backed the strike in a ballot.

Other unions have said they will not join in, however, among them the UFO union, which claims to be the main union for cabin crew and is demanding a 15 percent pay rise for its members.

Last week, Lufthansa was forced to cancel almost 1,000 regional flights at its Eurowings and CityLine subsidiaries after pilots walked out in a separate pay dispute.

Several German unions are seeking more pay after restraint in recent years as inflation spikes in Europe's biggest economy.