Customers and staff were forced to flee two retail park stores after fire swept through the buildings.
The blaze broke out in a Homebase store on the site at Aylesford, Kent, and then spread to a neighbouring Carpetright store.
There were no reports of any casualties but both stores were badly damaged as the blaze sent plumes of thick black smoke high into the sky over the area.
Customers and staff were evacuated from the site as around 100 firefighters tackled the fire. Eyewitnesses described how the blaze could be seen from homes and roads surrounding the shopping centre.
Police closed the A20 in both directions between Maidstone and Larkfield and advised motorists to avoid the area. Residents were also instructed to shut windows and doors as a precaution, a Kent Police spokeswoman said.
Rob Rattenbury, 40, assistant manager at Carpetright, said thick plumes of smoke reached 50ft into the air when the fire was at its height.
He said: “We heard the alarm going off in Homebase so I got on the tannoy right away and told our customers to evacuate the store immediately. No one panicked, everyone just walked out calmly.”
He said there were about 30 shoppers in Carpetright at the time and around 50 in Homebase. He added: “Homebase is completely wrecked.”
Eyewitness Rachel Grigson, 37, said she was shopping in Sainsbury’s opposite the retail park when she became aware of the fire. The mother-of-two, who lives nearby, said: “I thought something must be going on and when I got outside I couldn’t believe it when I saw all the smoke.
“There was loads of really thick, black smoke, going right way up high into the air. People were saying they were worried it was going to spread to the other units as they’re all connected but I think they got there just in time to stop it.”