LAST UPDATED, 4 p.m.

SALT LAKE CITY (ABC4) — More than 70 firefighters were on the scene of a massive four-alarm construction fire near the corner of 1040 East and 2200 South in the Sugar House area this morning.

Authorities don’t yet know what caused the fire, which began on the top floor of an apartment complex that was under construction. No injuries were reported, as the construction area was unoccupied at the time the fire broke out. ABC4 has learned the structure was being built by Kier Construction of Ogden.

Salt Lake City Fire Department (SLCFD) stated this afternoon that the structure will be demolished starting at 5 p.m. today and will continue through the night until it is complete. This may have an impact on street traffic near the scene, firefighters said. Specifically, 2100-2200 S. Highland Drive and lower Wilmington Avenue remain closed to public access.

“The fire scene will continue to generate smoke,” stated department officials in a press release. “Residents who have respiratory concerns or others who are at high-risk of smoke contamination should consider relocating. Those high-risk individuals who are unable to or uninterested in relocating should don respiratory protection (N95 or better mask). All residents should ensure windows and doors are closed until the smoke subsides.”

Responders tell ABC4 the fire seems to have broken out on the top floor at around 11:30 p.m. Tuesday night, Oct. 25 but continued to blaze well into the morning hours today. Several floors of the construction area collapsed and explosions were reported within the structure.

Crews focused on evacuating nearby buildings, including neighboring apartment complexes the Sugarmont and the Vue, and much of the firefighting activity focused on keeping the fire from spreading to nearby structures. The heat from the fire, however, did shatter windows in some nearby structures.

SLCFD officials said select residents of Sugarmont and Vue will remain evacuated until the demolition is complete and the firefighting operations end. Residents who need to retrieve personal items from their apartments should meet with their building’s manager or with police officers to gain access.

The American Red Cross reported that they set up an evacuation site for more than 200 people this morning, though that number was downsized to under 50 later in the morning. Operations started at Forest Dale Golf Course but were later moved to the Church of Jesus Christ of Latter-Day Saints stake building at 2005 S. 900 East. Residents who need current information or Red Cross assistance should call 800-733-2767.

The blaze remains under investigation.