Hemel Hempstead Job Centre has been evacuated while firefighters investigate reports of a burning smell.
Two engines rushed to the Waterhouse Street building just before 12.45pm.
Alex Yiallouros, 18, of Wilkinson Way, Bennetts End, and Emma Relf, 35, of Curtis Way, Berkhamsted, were signing on at the time.
Alex said: “The power went down and the lights went off. Next minute, the alarms went off and all the staff went out and we just followed them.”
Emma said: “I was just getting ready to sign when the fire alarm went off and we were told to leave. They said it was an electrical fire or something.”
Herts Fire and Rescue Service spokesman David Henning said: “There was a smell of burning coming from the computer suite of an office.
“They are now using a thermal imagine camera to investigate.”