Fire investigation officers, building contractors and council officials will visit the site today to assess the damage.
The city centre was thrown into chaos after the huge blaze broke out in a four-storey building in Hanover Street just after 3pm yesterday.
Smoke billowed from the roof as workers from nearby businesses, including Thomas Cook and Yorkshire Bank, were forced to leave their offices.
Staff working for a catering company on Hanover Street were also forced to flee. They had been preparing for a lavish opening ceremony at the Assembly Rooms to celebrate an 18-month refurbishment, though the event itself was not disrupted.
At its height there were 60 firefighters tackling the blaze, and crews of around 40 from Lothian and Borders Fire and Rescue Service were expected to remain overnight to dampen down the scene, as investigations into the cause got under way.
It is not known where the fire started.
A fire brigade spokesman said the blaze had spread into an extension to the rear of the building, with suspected fires burning through hidden voids to offices and residential properties two storeys above.
There were fears the blaze, which saw areas of George Street and Princes Street closed off to pedestrians, would hit the official re-opening of the Assembly Rooms.
Euan Mills, 18, was in the Blue Arrow Catering offices, where he was helping to prepare for the event when the fire broke out.
He said: “We were told to leave and evacuated for our own safety – the smoke was pretty bad, it was coming out of Thomas Cook and going from white to black.”
Angeline MacLean, 26, who works with Blue Arrow Catering, said: “I have staff who are working in the Assembly Rooms so when I heard what was happening I rushed out to check that they were OK. You could see the smoke billowing out from behind Thomas Cook.
“I’m just waiting to get inside now – I have no idea what’s happening.”
A spokesman for the venue later said the event would go ahead as planned.
Crowds gathered behind a police cordon to watch as firefighters tackled the blaze.
Roads – already congested following the closure of York Place – were jammed, with Hanover Street and part of George Street shut off.
Mohammed Sleem, 31, had been working in his office at Waverley Lane. “We were sitting inside the office and then all this smoke started to come through, from the back windows. You could see the firemen trying to douse the roof,” he said.
“Then we got a knock on the door and the fire brigade told us to evacuate – we’ve been standing here ever since.”
At its height, crews used 11 appliances and three lines of hose to tackle the blaze.
The fire brigade said no- one had been injured in the incident.
WHAT THE BLAZES . .
THE MAJOR fire in Hanover Street was not the first to spark a huge response in the city centre.
One of the worst fires in living memory ripped through the Old Town in December 2002. More than 150 fire engines from across Scotland spent 52 hours tackling the blaze in the Cowgate.
In August 2007, a blaze in Princes Street brought the city centre to a standstill and caused £2 million of damage.
And in 2008, Princes Street’s Marks & Spencer was evacuated after a fireraiser set a rack of clothes alight.