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Towering smoke and spiraling embers filled the sky as an under-construction building project in downtown Salt Lake City turned into an inferno Sunday.

It took at least 60 firefighters a little more than an hour Sunday evening to douse a four-alarm fire at the building, at 550 E. 500 South.

No one was injured, and the cause of the fire is still under investigation.

A call came in at about 6 p.m. concerning the fire at the construction site. When firefighters arrived, they rushed into the building to extinguish the blaze, but soon realized that the rest of the structure was at risk of catching fire and coming down, said Salt Lake City fire spokesman Jasen Asay.

The exposed wood of the unfinished building allowed the fire to spread fast through the more than 40-foot-tall structure. Firefighters turned their priorities to keeping neighboring buildings safe as the multi-residential project went up in flames. Onlookers could feel the heat from half a block away.

"I've never seen anything like it before," said bystander Kitti Smit.

As swarms of embers floated north to the Smith's grocery store across the street, emergency responders evacuated the supermarket as a precaution. Firefighters doused the store's roof to keep the embers from catching fire.

Their concern also turned to a construction crane that reached over the building, Asay said. Firefighters kept the heat from damaging the crane too severely to prevent it from falling over.

The building project had been in compliance, and the construction company reported that the building did not have any utilities or source of heat yet, Asay said. The company added that no workers were at the site Sunday evening, Asay said.

He could not speculate about whether the building project is a total loss. The estimated damage is $1.5 million, according a fire department news release.

Hundreds of onlookers were gathered at the scene.

Among them, Scott Sanders said he had never seen a fire so massive. The flames were visible from Midvale, Sanders said.

"You could just feel the heat," said Sarah Preston, standing more than half a block from the smoldering building, enveloped in smoke.

A man in his 20s was detained for questioning after allegedly falsely claiming affiliation with the fire department, Asay said. He is not considered a person of interest in starting the blaze.

Police and firefighters closed off 500 South from 400 East to 500 East for more than an hour, which kept people at a distance and allowed a dozen firetrucks, engines and police cars to fill the road .

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