An emergency services veteran on Friday urged the community of Surfside, Florida to not lose hope as rescuers desperately search for survivors following the collapse of a 12-story ocean-front condo tower.

“You would be surprised how much people can survive, and that’s the case here. So we shouldn’t lose hope,” Carlos Castillo, who helped develop the Urban Search and Rescue Response System for the United States, told CNBC’s “The News with Shepard Smith.”

“I had a personal experience, the first time I responded was an earthquake in what was Soviet Armenia, at the time. We rescued a 60-year-old woman who had been trapped for five days, and she survived,” said Castillo, the chief development officer for emergency management company Tidal Group.

As of Friday evening, 159 people were still unaccounted for, and at least four people were confirmed dead. The rescuers are using jackhammers, picks, sledgehammers, shovels, and their own hands to dig through the wreckage. They’re using different types of scent dogs — including some that can sniff out bodies and others trained to smell people who are still alive. Rescuers also brought in heavy machinery to help pick up huge chunks of concrete and other debris.