The head of the country's largest company, Fonterra, says the growing Ebola epidemic could cost the company $150 million.

Chief executive Theo Spierings told TV3's The Nation today that as African countries locked down their borders in an attempt to control the disease demand was dropping for Fonterra products.

He was worried the disease would continue its spread across countries.

He says he has lived in West Africa, and it's very difficult to contain an Ebola virus or whatever virus to a certain region because people are used to travelling and crossing borders.

If the market in West Africa slowed down or dropped off that would affect 100,000 tonnes of powder.

Mr Spierings says that's about six percent of Fonterra's exports.