The collapse happened at the Pant Y Wal wind farm, with images showing part of the structure and its blades lying flat on the grass.
Its manufacturer said it is investigating what caused the turbine, which was 115 metres tall, to fall over.
Residents in the nearby Gilfach Goch, a small village in south Wales, said they heard a loud noise early on Monday morning.
Many said they thought it was thunder at first. One woman posted on a local Facebook page saying she thought it was a car crash.
Others said they heard the sound of the blades whizzing in the night before the bang happened.
A spokesperson for Nordex, the turbine manufacturer, said: “Unfortunately an incident occurred at the Pant Y Wal wind farm in Wales. On Monday 14th February 2022, a N90/2500 turbine collapsed.”
They said no one was injured by the event and the only material damage was to the turbine itself.
“A team of local Nordex specialists with experts from Nordex main office are currently investigating the root cause of the incident together with the wind farm owner. As yet, no reliable statement can be made as to the underlying cause of the collapse,” the spokesperson said on Wednesday.
The turbine had been in place at the wind farm since 2013.