Underground tunnels built at a historic Wigan mill during the Second World War have been sealed up.
The tunnels underneath the site of Pagefield Mill in Swinley were initially used to store ammunition.
But now they are abandoned, apart from children and urban explorers who delve into the tunnels to see what is there.
The entrance is in a wooded area and had been covered with a large rock, but that had been removed at some point by people trying to get inside.
The authorities were concerned that someone could get hurt inside the dark and dangerous tunnels.
So yesterday firefighters using specialist equipment searched the tunnels to check there was nothing inside.
Then the entrance was sealed up by Wigan Council to make sure no-one else could go in.
Wayne Van Hecke, station manager at Wigan fire station, said: “There is a risk to us and to members of the public from the tunnels underneath the mill.
We want to secure the tunnels to remove the risk to children and other people.”
The fire service, police and council did not have a lot of information about the tunnels and how far they went.
Before crews went into the tunnels, Mr Van Hecke said: “They were really well made but we can’t find any detailed plans of them or blueprints. We are treating it as a risk because we don’t know what’s down there.”
Sgt Adam Wall, neighbourhood officer for Greater Manchester Police, said: “We are hoping to do a sweep and clear. We will make sure there is nothing down there untoward and update information and intelligence about how far they go.”
More than 30 fire and police officers gathered at Pagefield Mill yesterday morning for the operation, along with council staff.
There were fire engines from Wigan, a technical response unit from Leigh and a command unit from Rochdale.
Four firefighters went into the tunnel, using breathing apparatus and lamps.
They used a new piece of equipment called Waysafe, which uses LED lights to show the firefighters’ route and can be used to raise the alarm.
Measures were put in place to strengthen the communication system while they were underground. After 25 minutes, the firefighters emerged to say they had searched the tunnels and did not find anything.
The tunnels were 50 to 60m-long, though parts had been blocked off in the past so they used to go further.
Mr Van Hecke said: “The tunnels were pretty much as they thought they were going to be. There were no surprises really. We searched them quicker than we thought we would do, which was really good.”
Marie Bintley, Wigan Council’s assistant director for growth and housing, said: “We are grateful to the crews from Greater Manchester Fire and Rescue service for using their expertise and time to give the tunnels the all clear.
The clearing and sealing up of the tunnels is another important step in reducing hazards on the site. We will continue to work with our partners in the fire service and the police to make sure the risk of the site is reduced.”