Teenagers hand themselves in over Sydney CBD fire

Two 13-year-olds have come forward in relation to last night's fire in the Sydney CBD.

Acting NSW assistant police commissioner Paul Dunstan said an arson squad has been investigating the blaze.

"Overnight of a group of young people that were seen running from the fire scene shortly after 4pm," he said.

"I can confirm that two young people handed themselves in at two separate police stations in the late hours of last night.

"We are speaking with these young people throughout the evening, and they are now assisting police with our inquiries."

While the building was being occupied by rough sleepers, police said there have been no reports of injuries to members of the public.

Remains of the building in Surry Hills are at risk of collapse, with road closures in place should the structure come down.