Hertfordshire Fire and Rescue Service have asked the public not to panic, as an emergency services training exercise takes place at St Albans Cathedral.
Police and ambulance crews will join their colleagues at the fire service this evening (Tuesday, October 17).
A "number of fire service resources" are expected to take part.
A spokesperson for the Hertfordshire Fire & Rescue Service said: "This evening we will have a number of Fire Service resources along with Police & Ambulance at St Albans Abbey for an exercise.
READ MORE
"Please do not panic as it is training. Thank you."
Fire, ambulance and police services can be contacted in an emergency using 999.
Phone numbers 101 (for police) and 111 (for healthcare) can be used in non-emergency situations.
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 The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.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