Local news sources said strong winds may have been a factor in toppling the 28-metre high rig.
The accident occurred at a construction site in the Kojimachi district in Chiyoda Ward. The piling rig, owned by Taiyo Kiso Co., fell over at around 11 am while pulling up a 6-tonne column for the basement of a 19-storey building under construction.
The machine injured two pedestrians, three people who were in a truck on the six-lane road, also known as Shinjuku Dori, and the rig's 38-year-old operator when it fell, the police said.
A woman in her 60s remained unconscious after being knocked down by the pile driver, and its operator suffered serious injuries.
Strong winds were blowing at the time, and the piling rig appeared to tilt in the wind, a passerby who witnessed the accident said.
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