The incident happened in Germany during crane load tests at the Liebherr construction yard in Rostock.
The crane was being tested on board an installation vessel due to be delivered to offshore specialist Deme.
Its collapse was caught on video and uploaded to YouTube.
The 5,000 tonne crane had recently been installed on the offshore vessel Orion 1 which was built in China and owned by Cosco (Qidong) Offshore Co Ltd.
The vessel was due to start work later this year at the Moray East wind farm off Scotland.
Deme said: “A serious accident has occurred on board of offshore installation vessel ‘Orion 1’ at the occasion of and during crane load tests.
“The vessel is under construction and owned by by Cosco (Qidong) Offshore Co Ltd.
“The vessel is moored at the quayside at the Liebherr construction yard in Rostock, with the crane undergoing several load tests.
“Reportedly, a few persons suffered minor injuries.
“The vessel is expected for delivery to Deme NV in the second half of May 2020.
“The crane has suffered significant damage, while damage to the crane and the vessel will be investigated in the upcoming days and weeks.”