Nobody was injured during the incident which took place at a McCarthy Stone site in Canterbury
The boom is understood to have twisted during its erection at New Dover Road shortly after 10.30am. The attached boom twisted, bending at a right angle to strike the ground close to a busy car park by the project.
According to Kent Online, an eyewitness reported seeing half-a-dozen workmen surveying the situation, while all other work on the site had halted.
The tower crane is understood to have been a JASO tower crane which was being erected using a mobile crane.
A spokesman for McCarthy Stone said: “We can confirm that there was an incident during the erection of our contractor’s tower crane at our new retirement living development.
“No one was hurt during the incident. Our health and safety team is attending the site immediately to assess the situation.”