A fire department spokesperson said late Tuesday that crews would remain at the fire throughout the night spraying water on the building as the core of the fire continues to burn.
The blaze was reported at 4:56 p.m. at Fourth and China Basin streets in Mission Bay. It is believed it began on the ninth floor. Investigators are already interviewing witnesses, but will not begin the search for physical evidence of the fire's cause until morning.
One firefighter was taken to the hospital to be treated for a minor burn. No other injuries have been reported.
The MB360 apartments were under construction and set to open in August. The building's sprinkler system had not yet been activated.
Many witnesses described intense radiant heat coming off the fire. Falling embers did also pose a threat to nearby buildings and at one point, a small fire broke out on a UCSF building terrace. It was quickly extinguished.
Just before 6 p.m., firefighters decided to pull back from the fire due to concerns about collapse. San Francisco Fire Chief Joanne Hayes-White says there is continued concern of about collapse on two of the streets and if such a collapse occurs, the department may lose a rig inside the fire perimeter.
One building across from the fire was evacuated because windows were breaking from the heat. At one point, all residents on the eastside of Fourth Street between China Basin and Mission Rock had been evacuated, but by late Tuesday some evacuations had been lifted.
Animal Care and Control arrived on scene to help to help with displaced pets. The Salvation Army and American Red Cross also sent teams to assist displaced residents and first responders.
Mayor Ed Lee issued a statement Tuesday evening thanking the firefighters for their efforts, saying in part, "I am extremely grateful and relieved that no one sustained serious injuries during this very serious incident. Thanks to the leadership and determined action of our Fire Department, the very real potential of severe damage to other homes, businesses, and structures in the neighborhood was avoided."
Third and Fourth streets from King to Mission Bay streets remain closed. Muni Metro service on the T-Third line has been impacted.
KGO-TV San Francisco, CA contributed to this report.