By Jackie Storer
BBC News, Stratford
The thick, black plume of smoke drifting high into the sky could be seen for miles across London.
Workers rushed to their windows, tourists turned their cameras skywards from as far away as Westminster and cars pulled over as screaming fire engines, with their blue lights flashing, demanded to be let through.
Meanwhile television companies sent helicopters whirring up as they broadcast pictures of the scene near Stratford, east London, live to the world's front rooms.
In a city still nervous of terrorist attacks after the 7 July 2005 bombings, this spiralling pall of blackness could probably only mean one thing.
But, thankfully, it turned out not to be terrorism.
A blaze had broken out in a disused warehouse on the site of the 2012 London Olympics, and initial reports were that no-one had been hurt.
From seeing the smoke to the first flames there was about five minutes and then the building collapsed about 30 minutes later
But the fact the smoke stretched into the heart of London caused news organisations from across the world to descend on the closest vantage points.
Security guards protecting the 2012 site made some routes almost impassable for journalists, rubber-neckers and the simply curious.
A canal footpath, popular with walkers en route to the Olympic development, was blocked by police cautious of potential explosions.
This forced about 20 or 30 reporters, photographers and cameramen to gather on a bridge in Eastway to get the best view they could, albeit some way away from the incident.
Meanwhile London Fire Brigade said it had taken more than 150 calls about the blaze in the empty single storey building after it was first alerted shortly after noon.
But to people living in this run down part of the East End - only a few miles from the Kray twin gangsters' haunts and the Blind Beggar pub - those few minutes of not knowing what had caused the smoke were frightening.
Eyewitness Paul Hallam, 50, a production worker at a nearby printing firm, said: "We were working in the office just the other side of the water.
"We noticed it was getting a bit misty outside and then it was getting more and more smoky.
"There were flames coming about 100ft high in the end. The whole of that building, about the size of a football pitch, went up.
"We could feel the heat through the glass. It was pretty fierce.
If the wind had been coming towards us it would probably have taken our building out as well. We just hurried to get out.
"From seeing the smoke to the first flames there was about five minutes and then the building collapsed about 30 minutes later."
Eye witness Danny Cherry, 30, a print worker, said: "We heard this small bang and came rushing out.
"What we could see was just so much smoke. People were saying it was the old bus depot, but I think it's actually an old clothes factory.
"It's an old building that they were going to knock down anyway."
Retired builder Joseph O'Halloran, from Forest Gate, was going to have a look at the Olympic site when he noticed the smoke.
"A bloke told me he saw the roof collapse and the flames were 100 feet high," he said.
"There has got to be something in the building for it to still be going. Somebody said there were gas cylinders in there."
Samson Bereket was taking his children Nimrod, three, and Michal, one, to play group close to Victoria Park, when he saw the blaze.
"I saw smoke going up and up and then I saw the flames. It looked like a really big fire so I took my kids home quickly," he said.
Hopefully, when his children are eight and six, they will be back for an altogether more enjoyable visit to the area - when the 2012 Olympics get under way.