WELLINGTON, Jan. 14 (Xinhua) -- New Zealand dairy company Synlait Milk said registration of its Dunsandel plant in the South Island has been renewed by Chinese authorities for another four years so as to feed growing demand for infant formula from Chinese customers.

The company, which makes about 8 percent of its sales in China, said the registration by China's General Administration of Customs (GACC) will enable the firm to continue exporting canned infant formula.

Synlait Milk is currently building a second infant formula plant in Waikato in the North Island. The increased capacity is needed to feed growing demand for infant formula from customers including China's New Hope Nutritional and Bright Dairy, as well as New Zealand-based a2 Milk Co and Munchkin.

Synlait renegotiated a supply agreement with China's New Hope Nutritional and Bright Dairy last year, with quadruple increase of sales over the next five years, according to Synlait Milk.

Bright Dairy owned 39 percent of Synlait shares, which have gained almost 32 percent over the last year.

"Re-registration is required every four years and included an in-depth assessment where Synlait was asked to prove it has robust systems for change management, pathogen management and food incident management," Chief Executive Leon Clement said in a statement on the company's website.

The three-day onsite audit conducted by New Zealand's Ministry for Primary Industries on behalf of GACC also included a full traceability exercise from raw materials through to export, as well as an assessment of Synlait's capability to meet China's rigorous regulatory requirements.

China has strict criteria which overseas manufacturers must meet to maintain registration, and Synlait Dunsandel continues to meet these high standards, Clement said.

Synlait first obtained a Chinese certification for canned infant formula for its Dunsandel site in September 2014, he added.