A video shows the terrifying moment ghost hunters fled a "haunted" fort as loud rumblings shook the building.
The group were on a ghost hunting tour around the tunnels of Fort Widley in Portsmouth, which are said to be home to various spirits, when the thunderous roar rocked the building.
The noise gets louder and louder, prompting the spooked group to flee.
It all happened just after group leader Debbie McAll tried to communicate with the spirit world.
Tony Ferguson, who captured the scene on camera, said: “At first I thought it was thunder but the noise was too frequent.
“Then the tunnels started to vibrate as the sound got closer.
“We had members of public with us and they looked terrified. I then realised this wasn't thunder.
“I started to feel anxious myself, as did everyone, as we were at the end of the tunnels and it just sounded like bombs going off.”
In footage captured by Tony, 37, the sound begins as a barely-audible boom.
Then, as the group discusses what they heard, they’re visibly startled by the boom repeating louder a second and third time.
“It’s like cannon going off,” says one person.
Finally the noise rings out a forth time, lasting for several seconds as Debbie rushes her group for the exit.
“The best way I could describe this is like a mini earthquake,” said Mr Ferguson, who’s nicknamed the Ghost Whisperer.
“No one knew what was going on.
“I don’t think anyone felt safe, as even Debbie – who knows this location inside out – looked worried.
“We left the area to get out in case the tunnels were collapsing or something.
“Debbie’s main concern was the safety of the members of public.”
Tony, a personal trainer by day, emerged from the fort to find a clear night sky overhead and no thunder.
When they re-entered the tunnels, he said, they were unable to recreate the sound they heard by banging on the walls or stomping their feet.
A second group visiting with Debbie’s organisation, Ghost2Ghost, had heard the noise in another tunnel and fled too.
Tony said: “So whatever this was vibrated through all three tunnels – that would take a hell of a lot of force.”
“I believe this location to be one of the most haunted locations in the UK.
“It’s a place I don't trust as there is something very dark and sinister happening within these tunnels.
“The atmosphere of all three tunnels is you always feel like you are being followed.”
Completed in 1870, Fort Widley is one of several Portsdown forts built to protect Portsmouth and its harbour from a potential land attack.
Its haunted reputation is legendary.
The spirit of a whistling sergeant-major is said to be one spooky resident, as well as the ghost of a disobedient drummer boy who fell to his death down a staircase while fleeing punishment.
A prostitute who was murdered at the fort is also said to roam the halls, apparently watching over the child ghosts.
