Bus and tram stations across Germany were at a standstill on Friday, disrupting millions of commuters and travellers, as 90,000 public transport workers were called out on strike to press for improved working conditions.

The strike, called by labour union Verdi in all federal states except Bavaria, is the latest in a series of industrial actions that has plagued the country's transportation sector in recent weeks.

"Strikes will take place from the start to the end of operations - generally from 3.00 a.m. (0200 GMT) on Friday to 3.00 a.m. (0200 GMT) on Saturday," Andreas Schackert, federal head of the buses and railways group at Verdi, said.

There are some exceptions, including Berlin, where a shorter seven-hour strike during the morning hours was announced.

Central to Verdi's demands are improved working conditions, it said in a statement, listing reduced working hours and increased holiday entitlement as requested measures.

"We have a dramatic shortage of labour in public transport and incredible pressure on employees. Buses and trains are cancelled every day in all fare zones because there are not enough staff," Verdi deputy chairwoman, Christine Behle, said in a statement on Monday.

Youth and climate movement Fridays for Future said 60 of its local branches supported the industrial action.

"We are striking together to mobilize for better working conditions and a future for public transport," a spokesperson said.

Commuter Bjoern Heinz Sacchet, standing in front of a closed subway station at Berlin's Alexanderplatz, was not impressed.

"I don't think much of it. In the end, it's the passengers who are affected, they don't get to their destination," he said.

On Thursday, a strike by security staff at 11 German airports affected 200,000 travellers and led to around 1,100 flight cancellations or delays, the German airports association ADV said.

Disruptions were set to continue in Hamburg, where Verdi called on ground service staff to strike from 3 a.m. (0200 GMT) on Friday until midnight.

The union said it was demanding higher paychecks and a one-time payment of 3,000 euros ($3,250) to adjust for inflation.

($1 = 0.9238 euros) (Reporting by Nette Nöstlinger, Klaus Lauer and Reuters TV Editing by Kim Coghill and Mark Potter)