Ten fire engines and around 70 firefighters tackled a fire in Chalk Farm Road on Friday.
The London Fire Brigade (LFB) was called at just after midday the ground-floor Louis Coca shoe shop and most of a first-floor flat roof had caught fire.
There were no reported injuries from the fire, which was under control by 2pm.
Ryan Salisbury, 30, said: “I was driving down the High Street at Camden, and from my vantage point, I could just see like a few small licks of flame coming out of the building.
“By the time I travelled probably about 500 yards down the road in the traffic, by the time I got to the corner where the fire was, the full roof of the one building was ablaze.”
A worker from the nearby My Village Café, who doesn’t wish to be named, started to see smoke at 12.15pm.
"Someone said there was a fire but I didn’t think it would be as serious as it was.
"Then everybody started panicking so I went outside and I saw flames and smoke. It was really scary to be honest," they said.
Smoke could be seen all the way from the Sir Richard Steele in Haverstock Hill, according to a member of staff at the pub.
Station Commander Brett Loft, who was at the scene, said: "Firefighters were working in incredibly hot and arduous conditions to quickly bring the fire under control.
"The brigade's deputy commissioner, Richard Mills, was passing by and noticed smoke coming from a building in the distance. He was first on scene and immediately began incident command.
"There was heavy smoke in the area and local residents were advised to keep their windows and doors closed."
The brigade's 999 control officers took 42 calls about the blaze. They used the 999Eye system feed smartphone footage from people at the scene straight to the control room.
Fire crews from Soho, West Hampstead, Paddington, Kentish Town and surrounding fire stations were at the scene, as was the London Ambulance Service.
The cause of the fire is under investigation.
The Ham&High was unable to contact Louis Coca for comment.
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