The so-called warning strikes started at 0100 GMT and kicked off union efforts to pressure employers into a nationwide collective labor agreement.

“Almost no buses, (underground) U-Bahns and trams are running,” Berlin’s transport authority said on Twitter.

In the southern city of Munich, no metros were operating and “only half of the buses are in circulation”, a spokesman for the MVG, which operates public transport, told AFP.

Meanwhile in Hamburg, metro services were disrupted and bus lines were not operating.

Regional and long-distance trains were unaffected.

Verdi is calling for negotiations for a collective agreement covering the 87,000 employees in the sector.

It says it wants an end to the unequal treatment of employees in Germany’s various regions and an agreement for common rules on holiday and bonus payments.

The Municipal Employers’ Organization (VKA), which represents public transport employers in Germany, has “rejected negotiations”, according to the union.

“The fact that employers are not even ready to negotiate mocks the employees… We only have warning strikes to signal how serious the situation is,” said Ms Christine Behle, vice-chairwoman of Verdi.

“Verdi’s behavior is irresponsible, particularly at this time of crisis,” the VKA said in a statement.

The strike movement is expected to end in most cities around 1000 GMT, although in some, such as country’s financial centre of Frankfurt, no underground or trams are expected to be in operation for 24 hours.

In Germany, “warning strikes” – coordinated walkouts of a few hours – are traditionally used as the opening shot in wage disputes with employers, before unions resort to stronger industrial action.