"As this market grows and as Asia grows its demand for dairy products, Fonterra intends to be at the forefront of that," he said.
"These are markets where, inevitably, as the consumer base gets wealthier, the demand grows not only for protein but for more security in its food and more quality in its food. And that's where Fonterra fits in."
Fonterra Brands president Achyut Kasireddy said Indonesia was one of the company's priorities.
"Our investment in this site allows us to produce more high quality dairy nutrition to meet Indonesians' increasing demand for dairy," he said.
The company also runs a scholarship programme for Indonesian farmers to help grow the local dairy sector.
Later today, Key will travel to Surabaya, the capital of East Java.
There, he will visit Baba Rafi, an Indonesian entrepreneur.
Key said the entrepreneur "started off from very humble means" and had built a business which had expanded into nine countries, using New Zealand beef.
"It's a good example of how a small start-up entrepreneur can build a global business," he said.
The Prime Minister will also launch a online competition to help young Indonesians to travel to New Zealand.