A two-story framework for the residential building in the New York City borough of Queens had been erected when the red crane toppled and went sprawling across it around 2:30 p.m. behind a big neon "Pepsi Cola" sign, a local landmark.
The three people who were seriously injured were in stable condition.
One person appeared to have a broken bone. Three people had to be extricated from underneath the crane, Deputy Fire Chief Mark Ferran said.
Preston White, 48, a carpenter from the Bronx, was on his first day on the job at the site in the Long Island City neighborhood.
He had turned to speak to a friend when he heard a popping sound and turned back around.
At that moment, "I saw the cable whipping toward the deck. ... You could just hear it buckling," White said.
The impact shook the scaffolding he was on.
The crane cut down the framework of the building "like a hot knife in butter," White said, because there was no plaster on it yet.
A fellow worker, Russell Roberson, 32, of Brooklyn, said the crane had been up about four days - and went down really fast.
City officials went up in a cherry picker while investigating the accident.
Construction cranes have been a source of safety worries in the city since two giant rigs collapsed within two months of each other in Manhattan in 2008, killing a total of nine people.
Those accidents spurred the resignation of the city's buildings commissioner and fueled new safety measures, including hiring more inspectors and expanding training requirements and inspection checklists.
Another crane fell and killed a worker in April at a construction site for a new subway line. That rig was exempt from most city construction safety rules because it was working for a state-overseen agency that runs the subway system.
During Superstorm Sandy, a construction crane atop a $1.5 billion luxury high-rise in midtown Manhattan collapsed in high winds and danged precariously for several days until it could be tethered.