The spokeswoman, Anna Maria Koch, 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 8 am.

“For four people, help came too late and they died at the site of the accident,” Koch said in a statement.

“The rescue measures are continuing. It cannot be ruled out that more people were buried by debris or injured.”

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

Some 150 emergency responders were at the site seeking to rescue anyone still trapped. 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-Überseequartier, 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.

‘Very complicated operation’

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,” it said.

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

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

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

A police spokesman said a probe would “take some time” as officers “have not yet been able to really reach the site of the accident”.

Rescuers were using heavy equipment to clear the rubble and recover other possible victims.

Karin Pein of the Hamburg’s department for urban development and housing thanked the emergency response teams, noting that they were carrying out a “very complicated operation” at the site “at a great deal of personal risk”.