Factory workers ran for their lives when a shisha bar on top of a factory burst into flames.
The blaze started at about 11am yesterday at Cloud 9, on the roof of Curzonia Knitwear, in Leicester.
More than 60 firefighters were at the scene as flames tore through the wooden structure, sending huge plumes of thick, black smoke – visible from 10 miles away – over the city.
The streets around the building, on the corner of Curzon Street and Birstall Street, St Matthew's, filled with spectators.
Leigh Bevans, 26, of Highfields, said: "I saw people on the floor below still at work in the factory. They didn't even realise there was a fire and some lads ran upstairs to tell them to get out."
The workers then fled the building, and the fire service later confirmed no one had been hurt.
Shank John, 25, who lives nearby, said: "I was in the building next door and I heard a man shouting, 'Fire, fire, fire' and we all went outside. I was very scared."
As the flames grew, a police patrol car drove up the street with an officer shouting out of the passenger window for the crowd to move back.
Fire crews managed to get up an exterior fire escape, while other firefighters on aerial platforms blasted water down onto the structure.
Nathan Earle, 20, of Fleckney, had seen the smoke from 10 miles away and decided to take a closer look, saying: "It's not often you see something like this."
Wasim Munshi, 19, of Evington, was among those watching the blaze.
Wasim said: "I've been to Cloud 9 and there's a lot of wood to burn, as well as the gas heaters. It's a popular place, too. It's a shame."
Ten firefighters in breathing apparatus entered the building and made their way to the fourth floor to prevent the blaze from spreading down through the factory.
Incident commander Matt Cane said: "It was spreading downwards and we needed to stop it moving to other parts of the building.
"Luckily, we were able to get it under control and prevent it from causing any more damage."
By 12.15pm the flames were shrinking and the black smoke was mixed with water vapour as the fire crews began to win their battle.
Ansle Grogan, 39, of Highfields, said: "The flames were huge at the height of it, and the firemen are so brave – rather them than me."
Fire investigators were last night examining the scene and said they believed the blaze might have started inside the shisha bar.
Mr Cane said: "It's too early to say what the cause was because the damage is too severe. It'll take a while establish exactly what happened."
Cloud 9 opens from 5pm until 2am each day, and is thought to have been closed at the time of the blaze.
A message on Cloud 9's Facebook site yesterday read: "Cloud 9 is closed down due to fire. Inshallah (God willing) will re-open soon."
Planning approval was granted in 2010 to change part of the building into a café with smoking shelter. In 2011, approval was given to expand the smoking area.
The city council's reasons for approving the application included that it was satisfied "adequate controls were in place to meet health and safety requirements".
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