Hundreds of flights have been cancelled across Germany as airport workers stage a nationwide strike over pay, posing a major disruption for air travellers.

The industrial action, led by the trade union Verdi, began unexpectedly on Sunday at Hamburg Airport, before expanding to a nationwide strike.

Passengers at Frankfurt, Munich, Berlin and other major hubs have been urged not to travel to airports, with operations severely disrupted. Frankfurt, Germany’s busiest airport, said passengers would be unable to board flights and transfer would “almost certainly” be affected.

Verdi, which represents public sector and transport workers, is in an ongoing dispute over wages and working conditions.

German media reports thousands of flights could be cancelled across the day, disrupting travel for more than 500,000 passengers.

The Lufthansa group, whose main hub is in Frankfurt, confirmed “delays and extensive cancellations” across all its airlines.

Meanwhile, Munich Airport warned of a “greatly reduced flight schedule”. This includes flights by Eurowings, Austrian Airlines and Swiss Air.

Katja Bromm, spokeswoman for Hamburg Airport, where all 143 departures scheduled on Monday have already been cancelled, said Verdi was “dishonourable” to call a strike without notice at the start of the holiday season.

She said that Sunday’s walkouts were “excessive and unfair to tens of thousands of travellers who have nothing to do with the disputes”.

A spokesman for Verdi accepted that the strike would affect many, but said the travel disruption was necessary to extracting a better pay offer.

Lars Stubbe, the union’s Hamburg representative, told the BBC: “The workers are aware that disruptions do happen, and they are uncomfortable with that, but in any case, it is the employer that caused these strikes because they haven’t put a negotiable offer on the table.”

Many of Frankfurt Airport’s 1,770 scheduled flights have already been cancelled, while the majority of Munich’s 820 flights are expected to be cancelled.

Hundreds more cancellations are anticipated across Stuttgart, Dusseldorf, Cologne and Berlin.

Many passengers had already checked in their luggage and were having problems getting it returned, according to public broadcaster NDR.

ADV, which represents major German airports, said the strike had “almost completely paralysed air traffic”.

Verdi’s demands include an 8% pay rise, or at least €350 (£294) more per month, for all workers – and three extra days of holiday, plus one additional day for union members.

Stubbe said that while airport wages range were above minimum wage, ranging from €13-€25 per hour, workers in different roles – particularly security staff – received less annual leave than others.

“There have been two rounds of negotiations in which the employers have not yet offered one penny,” he added.

“It is quite usual that we don’t get any offers in the first round, but now even in the second round, the employers have basically said, ‘No, we’re not going to give you an offer because we don’t have any money’.”

BDLS, the body which sets security workers’ pay, said in a statement: “The damage caused by this strike is almost exclusively to companies that are not at the negotiating table.”

It called on the government to outlaw short-notice strikes, adding that air transport was “essential for Germany as a business location” which “must not be exploited” in collective pay disputes.

Ralph Beisel, ADV’s general manager, said the strike was having an impact on European and global air traffic, leading to missed connections due to a “domino effect”.

He called for reforms to German strike laws concerning “critical” infrastructure.

The so-called “warning strike”, an established tactic in German wage negotiations, concerns two separate pay disputes: one relating to airport security workers, and a broader disagreement over pay for federal and municipal government employees.

Verdi has also called for strikes in waste collection across several German cities, including Berlin, Essen and Kiel, where bins have gone unemptied since last week.

Pay talks for government workers are set to restart on Friday in Potsdam, while the next round of talks for airport security staff is scheduled to begin on 26 March.

Niklas Benrath, of the VKA, which regulates pay and conditions for municipal workers, also criticised the strikes, saying Verdi’s demands would cost nearly €15bn.

“With a total municipal debt of around €160bn, these demands are not financially viable,” he added.