Alexander Retemeyer, a prosecutor speaking for investigators, said on Saturday they were looking at human error and what happened in the 32km track's control centre, where the required two employees were on duty.

They were supposed to make sure the maintenance vehicle was off the track by waiting for a radio call from other workers, and by checking the vehicle's garage themselves, Ratemeyer said.

Only then were they to turn on the electricity enabling the train driver to start.

The service vehicle was not shown on the same computer system that displayed the position of the maglev, or magnetic levitation, train, he said at the track's visitor centre, nor was the stretch of track where the accident occurred covered by video cameras.

The train's start "can only be cleared by visual and radio contact", Retemeyer said at the visitor centre at the track, used to showcase the technology.

"Many points along the track are controlled by video cameras. But the place where the accident occurred had no video surveillance."

Promise

Retemeyer declined to say whether the two control room workers had been interviewed.

Wolfgang Tiefensee, the transport minister, promised a "swift but thorough investigation".

"The question that we have to ask will be, was the security concept sufficient and was it followed step by step," he said.

"And then when we know what the reasons were, we will be able to draw conclusions."

Ewald Temmen, the police spokesman, said prosecutors, who are in charge of the investigation, would go over the scene Saturday with technical experts while investigators sought to identify all the victims.

All 23 of the dead had been positively identified, officials said.

Some of the 10 injured had already been able to leave the hospital and those remaining had injuries that were not life threatening, said local councilor Harmann Broering.