Police later confirmed that a 59-year-old woman succumbed to her injuries at the scene.
Two other employees of the company, aged 55 and 62, were seriously injured.
A spokesperson for the company would not comment on the report and referred questions to the police, who confirmed there had been an attack but did not name the utility company.
The attacker, a 21-year-old male, was apprehended by police at the crime scene. He was swiftly taken into custody for interview.
Police have not yet established a motive for the attack but told German media: ‘Caring for the injured is our top priority, as is clarifying the exact circumstances of the crime.’
The incident comes weeks after 17 people were injured in a horror train station knife rampage in Hamburg – with four victims left in intensive care.
Police arrested a 39-year-old female suspect in connection with the stabbing spree at Hamburg Central Station on May 23.
The suspect was believed to have acted alone and there was no sign they had a political motive, police said.
Officers ‘approached her, and the woman allowed herself to be arrested without resistance’, Hamburg Police spokesman Florian Abbenseth told journalists in comments carried by public broadcaster ARD.
‘We have no evidence so far that the woman may had a political motive,’ Abbenseth said.
‘Rather, we have information based on which we now want to investigate whether she may have been experiencing a psychological emergency.’