Ofi Osin-Cohen and her husband were asleep in their Surfside, Florida, apartment when they were startled awake by what sounded like thunder — and then they felt the 12-story building shake.
The couple were among the more than 30 people who were rescued Thursday morning after the Champlain Towers South condominium partially collapsed. At least one person was killed and 99 are unaccounted for as of Thursday afternoon, authorities said.
"It could have been thunder but it didn't really sound like thunder, and we felt the building shake," Osin-Cohen told NBC's "TODAY" show. "And we knew something was up. It rattled us."
She said she got up and looked out the window toward the street and saw "a plume of smoke coming up." Shortly afterward, a police car pulled up and an officer got out and started looking around with his flashlight to figure out what happened.
Still unsure of what caused the building to shake, Osin-Cohen and her husband got dressed, grabbed some essential items, and opened the front door of their apartment hoping to escape down the hallway.
"All I saw was debris," she said. "Debris was covering the door next to us."
The couple made their way to a nearby stairwell and tried to exit on the pool deck, but the door was jammed, Osin-Cohen said. They then went down to the garage, but it was "full of water up to our ankles," she said.
"We didn't know what was going on at that point, and we realized that we weren't going to be able to get out through there either, so we decided to go back up the stairs," she explained.
As they made their way back to their apartment, Osin-Cohen said they encountered an elderly couple trying to find a way out. She and her husband took the couple with them and waved down firefighters from the balcony of their apartment.
Rescuers used a ladder and bucket to bring the four of them to safety.
"They are heroes. They're just unbelievable human beings," she said.
Osin-Cohen told "TODAY" that it was "overwhelming" to see the amount of damage to the building. She said as she and her husband were trying to exit, they could hear people screaming but she couldn't tell where it was coming from.
"I just wish heartfelt condolences to those who lost loved ones and prayers for those who need healing," she said.
Authorities received a call around 1:30 a.m. ET about the collapse. Raide Jadallah, the assistant chief of operations for Miami-Dade Fire Rescue, said of the building's 136 units, 55 of them in the northeast corridor collapsed.
Thirty-five people had been pulled from the collapsed part of the building, and two other people were rescued from the rubble, Jadallah said. There has been one fatality, officials said.
Commissioner Eliana Salzhauer said that the search and rescue could "play out for days."
One of the people pulled from the rubble was a young boy. Video obtained by NBC Miami showed firefighters carrying the boy away from the destruction and placing him onto a stretcher. His condition was not immediately clear.
Nicholas Balboa said he was walking his dog in the area and saw the condominium collapse. He said that the ground shook and he heard what sounded like thunder.
When the ground shook a second time, he said he knew something was wrong. Balboa said he took his dog inside and then walked toward Champlain Towers South. He said police were moving people away from the front of the building, so he walked along the beach toward the back.
According to Balboa, police and firefighters had not yet made their way around to that part of the building. As he and another onlooker moved closer toward the damage, he said he could hear someone yelling.
"I was able to see movement, so I saw the little boy's hands sticking up through the rubble as he was yelling to find him," he said. "Myself and the other individual, we began to try and make our way to him."
Balboa said that the boy was saying, "Please don't leave me."
"I was just letting him know, 'Hey, we're here. We're not going to leave you,'" he said.
Balboa signaled for firefighters who were able to rescue the boy.
Another witness, Fiorella Terenzi, said that she heard the collapse from her apartment one building away.
"I can't believe it. Still right now, what I saw. The building I used to see was not there," she said on MSNBC.
Terenzi said they have been without electricity and water since 1 a.m.