The ice formed upstream in recent weeks during a cold snap that saw temperatures plummet to minus 15 degrees Celsius.

Icebreakers have since smashed through the ice, sending the floes downstream where they accumulated at a barrage at Geesthacht, near the river-port of Hamburg, said Tilman Treber from the federal navigation authority (WSV).

Over the past few days, they have piled up and formed jagged piles up to 10 metres (more than 30 feet) high -- creating ice formations on a scale unseen for about 10 years, Treber told AFP.

The Elbe flows for more than 1,000 kilometres (about 680 miles) from mountains in the Czech Republic through Germany and enters the North Sea at Cuxhaven, downstream from Hamburg, Germany's biggest port.

On Monday an AFP photographer saw dozens of curious locals taking advantage of sunny weather to walk among the ice blocks washed up on the riverbank.

Treber said that on this stretch of the river breaking up the ice blocks is more complicated and only possible when the river current is stronger than the tide when it pushes briny water up from the North Sea.

The WSV said it's difficult to say when the river will become fully navigable, as temperatures are expected to drop below freezing point again.

Hamburg port authorities meanwhile said navigation hasn't been blocked in the city harbour thanks to the deployment of several icebreakers last week.