An 18-year-old man has been arrested on suspicion of arson after a fire in the Church Street area of Belfast.
The blaze was reported at around 5.40am on Monday.
Police officers are still at the scene, along with the Northern Ireland Fire and Rescue Service.
A number of diversions are in place and the public are being advised to avoid the area where possible.
Anyone with any CCTV or dash-cam footage from the area at the time is advised to contact police.
The building hosts a number of small creative businesses.
Tina Calder, owner of Excalibur Press, which has offices in the building, said: "I got a call this morning just before 6am. My brother is a security guard at the Ulster University and he said, 'Tina, your building is on fire'.
"Of course, I sprang up, got a taxi, came in and literally for about an hour and a half, just stood here crying watching the building go up in flames.
WATCH: Tina Calder speaking to UTV:
"I was able to give them keys, ring the landlord and the agent, and I made contact with the other tenants in the building as much as possible.
"It was just heartbreaking as I watched people's studios go. One man owns a violin making studio - it was gone. There are illustrators in there that have artwork.
"We can see that our offices are probably going to have significant water and smoke damage. All five of my staff are working from home today."
Ms Calder added: "We've had a wonderful outburst of support from the community here in Cathedral Quarter, asking what can they do to help, and it's just wonderful to see that community come together to support us."
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