BERLIN, Germany - At least three workers were killed in the northern German city of Hamburg on Monday when a scaffolding collapsed at a building site, with a fourth person believed trapped in the rubble, a fire brigade spokeswoman told AFP.

The spokeswoman said a fifth labourer had been critically injured in the accident, in which the scaffolding suddenly broke apart in an eight-storey-high elevator shaft shortly after 0800 GM

The fire brigade had initially said that five labourers had been killed and an unspecified number were buried in the wreckage of the disaster. The cause of the collapse was not yet clear.

"The rescue operation is running in high gear," the spokeswoman said.

Some 70 emergency responders were at the site seeking to rescue the trapped worker. The nationality of the victims was not yet determined.

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

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

The district combines new high-rise buildings with cafes, bars and riverside plazas designed to convert a previous industrial area into a lively quarter of Germany's second city.

'Highly dangerous'

Parent company Unibail-Rodamco-Westfield said in a statement sent to AFP that a "tragic accident" had occurred and that it was "supporting emergency responders and working with the authorities".

"Our thoughts are primarily with the victims and all those who work at the building site" which has been fully evacuated, it said.

"The rescue workers are on the scene and working closely with the police."

The daily Bild said the scaffolding in a building elevator 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.