State-owned power generator Mighty River Power is to buy a cornerstone stake in Christchurch-based turbine maker Windflow Technology.

Windflow is listed on the stock exchange's alternative NZAX board, and the Mighty River deal to take an almost 20% stake requires shareholder approval.

The Christchurch company is building 50 turbines for a New Zealand Windfarms project. Mighty River hopes to use the company's turbines for its first windfarm proposed near Wellington.

Windflow Technology chief executive Geoff Henderson says the deal is a vote of confidence in the company.