A German court delayed a long-awaited ruling on Thursday on the proposed dredging of the river Elbe for large container ships in Hamburg, Germany's largest port, saying it would wait until the European Court decided on a similar case.

Hamburg wants to make it easier for new generations of large container ships to reach its port regardless of tides in the face of intense competition from Rotterdam, Antwerp and Bremerhaven.

But green groups BUND and NABU lodged a legal complaint more than two years ago, arguing the environmental impact would be devastating as a result of dumping large quantities of mud and sand on fragile coastal wetlands.

The Federal Administrative Court in the city of Leipzig had been expected to announce a ruling on Thursday but said it would wait until the European Court of Justice rules on a similar case for the German river Weser. That decision is due next year.

The city of Hamburg and federal waterways authorities want to dredge about 130 kilometers of the river so that container ships with 14.5 meters draught can reach the port, against 13.5 meters at present. It would be the sixth time the river has been deepened.

Ship sizes have grown from vessels carrying 2,000 to 3,000 standard twenty foot cargo containers in the 1980s to ships carrying up to 18,000 containers today.

Some of the largest ships currently have to endure a costly wait for high tides to dock in Hamburg and the city fears shipping lines will switch to other ports if the Elbe is not deepened.