The Poundstretcher store in Blackwood is being demolished following a blaze in the early hours of Wednesday morning.
South Wales Fire and Rescue Service say the cause of the fire was bins being set alight.
Fire crews were called out at around 2 o'clock this morning.
Officers say refuse bins were on fire and this had spread to the store room at the back of the shop.
Due to safety concerns the High Street was closed and the electricity supply to a number of shops was cut. Structural engineers were called out to assess the safety of the building.
A Blackwood employee who works at the store next to PoundStretcher, which caught fire in the early hours of this morning, said crews did 'a brilliant job' in tackling the blaze.
Nicola Lambert said crews had managed to contain the flames so the fire didn't spread, but her shop had suffered some water damage following the incident.
"We'll work hard to open again," she said.
"It was a bit of a shock - it wasn't what I was expecting when I got up this morning."
VIDEO: Fire crews have been tackling a large blaze in Blackwood this morning. They were called to the scene in the early hours.
The fire service say investigators will be arriving at the scene of this morning's blaze at Blackwood's Pound Stretcher store shortly to begin an investigation into the blaze.
Crews will spend the rest of the day dampening down the building say officers.
The High Street is closed because of a building fire between Libanus Road and Pentwyn Road.