One person was taken to Edinburgh Royal Infirmary for treatment after the fire broke out shortly before 6:20am on Tuesday, while a number of businesses in the street have been closed until further notice.
Pictures shared on social media showed smoke billowing from buildings on both George IV Bridge and Candlemaker Row.
It is understood the alarm was raised by a cleaner at the Elephant House cafe, where JK Rowling wrote sections of her Harry Potter books.
Police closed several roads in the city’s Old Town on Tuesday morning, resulting in traffic building up in the area.
A fire service spokesperson said crews were dealing with thick smoke throughout the day, which prevented them easily entering the buildings to tackle the flames, making it difficult to establish the seat of the fire.
The spokesperson said that by late afternoon, 26 fire appliances had attended and that “well over'' 100 firefighters had attended to extinguish the fire throughout the day.
Incident commander David Farries, Scottish Fire and Rescue Service’s deputy assistant chief officer, said: “This is undoubtedly a complex and challenging incident.
“I would like to thank our crews as they work to extinguish the fire. I would also like to thank our emergency services colleagues and local authority partners.
“We will remain in attendance for a considerable time yet as we work to contain the fire.”
The fire service, which labelled the incident a ‘level four’ blaze, asked local residents to keep windows and doors closed due to smoke and advised people to avoid the area to allow access for emergency services vehicles.
Flats above Patisserie Valerie were evacuated and Candlemaker Row and Chambers Street were also closed. The Central Library, which is on the street, was also shut on Tuesday.
One eye-witness said they saw smoke coming out from the doors of Patisserie Valerie, and that water was being dispersed by firefighters into the Elephant House cafe and onto the building’s roof.
Early on Tuesday afternoon, unconfirmed reports emerged of the fire being trapped between the floor of the Elephant House and the ceiling of a flat below in Candlemaker Row.
Elephant House cafe owner David Taylor said the fire had not spread to the building, but it had suffered smoke and water damage.
He said he was “absolutely gutted” given the possibility of structural damage and because trade had just recently been returning to normal after Scotland’s recent lifting of Covid restrictions.
The Oz Bar in Candlemaker Row, below Patisserie Valerie, also suffered water damage. Oz Bar owner Tom Ponton said they had just refurbished the pub and were back to trading well again after two years and described the fire as “devastating”.
A 22-year-old resident, Marco, lives above Oz Bar and said their building was evacuated by firefighters after the alarm went off for a second time on Tuesday morning.
Lothian also said buses traveling along George IV Bridge were diverted, including the number 23 and 27 services.
Edinburgh City Council leader Adam McVey described the scenes as “terrible” and said council teams were working closely with emergency services to respond to the fire and minimise disruption.
Mr McVey said: “Our resilience team are also continuing to liaise with the relevant agencies and shared repairs’ officers are on site to offer structural engineering advice.”
Trade recovery made ‘much harder’
The Federation of Small Businesses (FSB) also thanked emergency services for tackling the fire.
Andrew McRae, FSB policy chair and business owner in the affected part of Edinburgh, said: “It is the hope of all Edinburgh locals that no-one has been seriously hurt in this dreadful incident.
“While it is too early to talk to the business impact of the fire, FSB stands ready to work with local firms and government at all levels to get this historic area back on its feet.
“It has been a hard 18 months for many Edinburgh businesses and today’s fire will make recovery that much harder.”
On Tuesday, an ambulance service spokesperson said: “We received a call at 6:39am to attend an incident at George IV Bridge in Edinburgh with our first resource arriving on scene at 6:46am.
"We dispatched two ambulances, one paramedic response unit and our special operations team to the scene.
"We transported one patient to Edinburgh Royal Infirmary.”
Tuesday’s blaze also sparked a large public reaction on social media, with many expressing their distress while thanking the emergency services for their efforts.
Photographer Matt Donlan, who captured many dramatic pictures at the scene, said: “On days like the one we are witnessing today, you can’t help but praise our fire service heroes. They’ve been on the go a long time in challenging conditions on a very warm day.”
Angus Robertson, SNP MSP for Edinburgh Central, also wrote: “Very sorry to see extent of fire in central Edinburgh. Thoughts go out to everyone affected and appreciation to the emergency services.”
Ian Murray, Labour MP for Edinburgh South, wrote: “Dreadful to see another fire in Edinburgh’s Old Town. I hope everyone is safe and the damage minimal.”