Emergency services were called to Swingate House in Stevenage after a planned demolition reportedly “went wrong”.
Firefighters and multiple police were spotted near Stevenage town centre.
“Demolishing gone wrong,” said one resident on Twitter.
Another reported a “big cloud of dust”. They added: “Glad I want driving past when that happened.”
A spokesperson for Hertfordshire Police said: “We're currently assisting at the scene of a building collapse in the Swingate area of Stevenage.
“A cordon has been put in place as a precaution and people are asked to please avoid the area at this time.”
A Stevenage Borough Council spokeswoman told The Comet: "Please stay away for the Swingate House area, the building that is being demolished has collapsed.
"The police are at the location and surrounding roads have been closed. We are assessing the situation and our priority is to keep everyone safe. We will keep you updated with any further developments via social media."
A spokesperson for the Hertfordshire Fire and Rescue Service said: "We are currently attending an incident in Swingate, Stevenage, where a building that was being prepared for controlled demolition has unexpectedly collapsed.
"We are not currently aware of anyone being injured."
For the most up-to-date information about the county's roads, visit our LIVE Hertfordshire traffic map.
Join our Hertfordshire Travel Information group on Facebook for all the latest traffic news in Hertfordshire.
Do you have a live or breaking news story from across Hertfordshire? Email: hertslivenews@archant.co.uk
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here