The move reflects the growing local-content requirement specified in the country's renewable energy procurement programme.
Gestamp first announced it would open a tower factory in South Africa in 2012.
The factory, located in the Atlantis suburb of Cape Town, should be operational by the end of the year, representing a total investment of around EUR 22 million. It will employ more than 200 people.
GRI chief executive Javier Imaz said: "With this new facility, GRI consolidates its position in the South African market, a factor that will enable the business to deploy and share its know-how to the local market."
Gestamp has a 60% stake in the 74MW Nobelsfontein wind farm currently under construction in Northern Cape province, using Vestas turbines.