Sixteen people were injured after a slab of wet concrete collapsed on the 24th floor of a high-rise building just across the Potomac River from Washington, officials said.
Three people were listed in critical condition, four were in serious condition, and the rest had minor injuries.
Earlier, officials had feared several construction workers may have been trapped under the concrete. At a news conference, authorities confirmed everyone had been accounted for.
Oscar Moscoso, a worker at the site, told reporters at the scene that he pulled out six people with his hands and shovels after the collapse.
He said he believed the accident occurred because the concrete on the scaffolding was too heavy.
NBC News’ Andrea Mitchell reported that the incident was being looked into by authorities and could turn into a federal investigation.