A council has stopped demolition work at a former mines rescue station near Wrexham which campaigners have been trying to preserve.
Wrexham council said a safety certificate was needed before work could continue at the building.
Heritage body Cadw recommended the 1913 rescue station for listing following a campaign, and a consultation was launched two weeks ago.
However, this does not prevent the owners from demolishing the building.
Campaigners say the rescue station is an important part of Wrexham's mining heritage, amid fears it could be turned into flats.
Councillor Phil Wynn said: "I had a telephone call from one of the local residents at about midday to say a digger had gone in and the gates had been locked afterwards.
"I rang building control and they said they had not received a Section 80 form off the land owner to commence demolition.
"Therefore, a Section 81 form had not been issued by the council for them to commence.
"One of the building control officers went straight down there, but that was 45 minutes after, and the digger had done significant damage to the training gallery."
Mr Wynn said the training gallery was one of the most historically important features of the building, and damage to it was "really very sad".
Planning permission to demolish the building was granted two years ago.
However, Clive Nicholas, the council's planning policy manager, said a safety certificate was needed to show nobody was at risk.
The mines rescue station was opened to help find survivors of mining accidents.
Those who trained there helped in the mission to rescue miners from the 1934 Gresford disaster, when an explosion claimed the lives of 266 people.
The centre closed in the 1980s and was handed to the fire service, but it recently passed into the ownership of businessman and former Wrexham FC chairman Neville Dickens.
Cadw recommended it for listed status, and a four-week consultation started two weeks ago.
However, the consultation period does not prevent the demolition of the building.
Mr Dickens has been asked to comment but it is understood he is abroad.
Malcolm Williams, a former mines rescuer, was one of those hoping to preserve the building.
Speaking before demolition began, he said: "If there was an accident in the pit you are crawling over debris and it is very, very difficult, but at the end of the day this place gave us the training we wanted."