Firefighters and police officers arrived at the building just west of Interstate 95 near downtown Miami after receiving calls about a fire around 8:15 a.m., and began rescuing residents from the building's balconies, Miami Mayor Francis Suarez said during a news conference.
Suarez said arriving first responders also found a man with gunshot wounds at the scene. He was taken to a hospital, where he was in critical condition. Officials said the shooting is part of an active investigation. They offered few other details, other than calling it an "isolated incident."
Officials later said a suspect in the shooting was taken into custody and likely started the fire.
Three firefighters were transported to Jackson Memorial Hospital due to heat exhaustion and were in stable condition, Suarez said during a news conference. Two have since been discharged, said Lt. Pete Sanchez, a spokesperson with the City of Miami-Fire Rescue. In addition, at least one resident was being treated for smoke inhalation, he said.
The gunshot victim, whose name has not been released, was listed as critical, Sanchez said.
Atlantic Housing Management, the company that manages Temple Court apartments, said in a statement that one of their employees was found shot inside the complex.
"We are still determining the cause of these events, and we are checking for other injuries. Police are investigating, and we will help in whatever ways we can," the management company's statement said. "We are grieved by all that has happened today, and our thoughts and prayers are with our team member and his family and residents of the Temple Court community."
News helicopters showed flames rising from the building along with large plumes of smoke several hours after the fire started. At least two ladder trucks were pouring water and foam onto the building.
The apartment complex consists of one-bedroom and studio units near the Miami River.
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"It was a wood-frame structure which explains the intensity," Sanchez said.
As of early evening, Sanchez said the fire "was under control and no longer spreading, but it still needs to be extinguished."
Residents from the building, many of them elderly, were taken to a staging area where they were offered food and any medications they needed, Suarez said. He added that at least 20 people had been processed and were rehoused with family, and some 20 more were expected.
"Our hope is we will be able to place them in permanent housing as quickly as possible," he said. "Obviously people are very emotional. They might not be able to get anything that was in those units. Some are worried about their pets. It's been very upsetting, very traumatic."
Suarez urged those who would like to help those impacted by the fire to contact the American Red Cross.
Smoke from the fire was also drifting over Interstate 95, and much of downtown Miami.
It was not immediately known whether anyone was injured in the fire.
Frisaro reported from Fort Lauderdale, Florida, and ABC News contributed to this report.