At least five workers were killed in the northern German city of Hamburg on Monday when a scaffolding collapsed at a building site, a fire brigade spokesman said.

Other labourers were still thought to be trapped under the wreckage from the accident, which occurred shortly after 0800 GMT.

"Several people are buried under the scaffolding and are considered missing," the spokesman said. "Five workers died at the scene of the accident."

Some 70 emergency responders were at the site seeking to rescue those trapped in the rubble. 

"It is not immediately clear what caused the scaffolding at the construction site to tip over," the fire brigade spokesman said.

The accident occurred in HafenCity, a once scruffy port district that has become one of the biggest urban construction projects in Europe.

The daily Bild reported that the scaffolding came down at the Westfield Hamburg-Ueberseequartier, a nascent business, residential and leisure development that is to include a major new cruise ship terminal when it is completed early next year.

The company could not immediately be reached for comment.

Bild said the scaffolding in a building shaft came down on at least eight workers.

The entire construction site was evacuated, including some 700 workers, Bild said.

Police at the scene cordoned off the site with tape and a rescue helicopter and several ambulances arrived to transport injured workers recovered from the wreckage.

Public broadcaster NDR said the workers had fallen from the eighth floor of a building under construction. It said rescuers were using heavy equipment to clear the rubble and recover other victims.

It quoted a fire brigade spokesman as saying that the rescue work itself was highly dangerous for the staff at the scene.  

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