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Video shows a young boy being pulled from the rubble of a South Florida condo building that partially collapsed early Thursday. A mattress could be seen near the boy as he was rescued and placed on a backboard.

Thirty-five people were pulled from the building — a portion of which was still standing on Thursday — and two people were pulled from the rubble, officials said. One person has been confirmed dead, and 51 people are unaccounted for, according to officials.

Watch the video:

The portion of the 12-story building that fell to the ground included dozens of units. 

Nicholas Balboa said he felt the ground shake and at first, it sounded like a storm or thunder. He ran a block to the scene of the collapse, CBS Miami reports, and said he heard someone in the debris, yelling.

“What he was actually saying was, you know, ‘Can you see my hand. Can you see my hand,’ and I could see a little hand sticking up, waving, and moving his fingers trying to get our attention,” Balboa said.

Balboa said the boy looked “fairly alright” when he was pulled from the rubble — “he had a guardian angel for sure.”

Charles Burkett, the mayor of Surfside, Florida, said there was no reason to believe the building wasn’t “substantially full” at the time of collapse.

“We’ve got probably a third or more of the building that is completely pancaked in the back,” he told CBS Miami.

The mayor called the situation “unspeakable” and said he believed people were still trapped in the rubble.

“You don’t see that in the United States. You don’t see buildings falling down. You might see that in third world countries. But there is something really wrong here that we’ve got to figure out,” he said.

The cause of the collapse is unknown.