Shoppers were left shocked when paving stones were suddenly overturned and a 'huge bang' was heard in Sunderland city centre.
The incident happened outside Arizona nightclub, in Holmeside, at about 11am today.
Coun Kelly Chequer, her daughter Millie Laws, 12, her friend Heather Marshall and her daughter Chloe, two, were walking past at the time.
Coun Chequer said: "We were walking down from Park Lane towards Holmeside, where Arizona is, when we heard a huge bang and a plume of smoke was sent into the air.
"Initially we were shocked and didn't know what had happened.
"No one appeared to be panicked or shaken, because there were no flames.
"As we got closer, we realised there had been some kind of explosion, and that the paving stone had lifted.
"It was quite alarming, because people were still walking very close to where it happened.
"We asked people to move away and I called the fire brigade."
The fire brigade attended, but say they did not need to carry out any work at the scene as there was no fire.
Engineers from Northern Powergrid are now believed to be working on the issue.
Coun Chequer added: "It's very lucky that no one was standing on that paving stone at that time.
"The paving slabs left the ground by quite a way. They lifted and moved.
"Anyone who was nearby was very lucky that they didn't get hurt.
"It's not what you expect to happen on a casual shopping morning in the city centre."