Enercon stated it does not know why this happened during the final stages of installing the E115/3.0MW turbine at the 21MW Borchen-Etteln site in north-west Germany last week (Thursday, 8 March).
Investigations into the incident are under way, the company confirmed, and an "independent expert inspector" will be asked to examine the cause of the damage.
A spokesman for the manufacturer said: "For reasons still to be clarified, the wind energy converter, which had not yet been commissioned, went into overspeed. This was when the damage to the rotor blades occurred."
Anti-wind group Gegenwind-Borchen, meanwhile, has shared pictures of the broken turbine on its website and claimed glass-fibre particles from the blades have contaminated a radius of more than 800 metres.
An Enercon spokesman said nobody was harmed in the incident, the wind energy converter has been "secured", and the scene of the accident has been blocked off.
The spokesman added: "Following completion of the investigations, the damaged wind energy converter will be repaired and commissioned as quickly as possible.
"All measures will be conducted in close consultation with the responsible authorities."