A brief warning demonstration strike by 12,000 dockers halted cargo movement for one late shift at the ports of Hamburg, Bremerhaven, Wilhelmshaven and Emden.

This was the first strike at German ports in decades and was slammed by management's Central Association of German Seaport Companies (ZDS) negotiator Ulrike Riedel as "not doing justice to the collective bargaining".

Negotiations between German port employers and the dockers union ver.di ended after 10 hours with the union rejecting the ZDS offer.

"This offer is far below the real wage protection demanded in view of the current rate of price increase of 7.9 per cent, and is therefore unacceptable," said ver.di negotiator Maya Schwiegershausen-Gueth.

"We have a comparatively high wage level in German seaports. In the last round of negotiations, given the currently challenging inflation rate, we made an offer that compensates for the losses of our employees in real wages," she said.

"This offer is in line with many other current ver.di collective bargaining agreements. The fact that strikes are now being called in the current crisis framework is completely unacceptable," said Ms Schwiegershausen-Gueth.

She said there was "a large wave of delayed ships" expected at German ports in the coming weeks, which would add further stress to the supply chain.

Ocean carriers using Hamburg's main container hubs, at HHLA and Eurogate could divert ships, but Rotterdam and Antwerp are heavily congested and will be unable or unwilling to handle transhipped German imports.

Maersk said its hubs at Bremerhaven and Rotterdam were its "most severely congested north European ports" and its networks were operating "under severe pressure".

Hapag-Lloyd said yard occupancy at Hamburg's Container Terminal Altenwerder (CTA) stood at 90 per cent, "mainly caused by the discharge of heavy import vessels and reduced import pick up rates".