A company that traded in gold and precious metals in under investigation by the Serious Fraud Office.

The SFO says a formal probe was launched into Grace Holdings NZ Ltd, trading as Bullion.Buyer.co.nz, after a number of complaints from investors last week.

"We have concluded that there are reasonable grounds to believe that an offence of serious fraud may have been committed, and accordingly commenced a formal investigation," SFO chief executive Adam Feeley said.

He says the SFO had secured the company's financial records.

The SFO wanted to contact as many investors as possible and was co-ordinating its investigation with other agencies.

Mr Feeley says it is liaising with the Registrar of Companies to ensure company funds are protected.

The company has been liquidated and a note on its website blames a former trader for its financial woes.

"The company's failure was primarily the result of actions taken by Elijah Gus Geldman who was formally (sic) one of our traders. Mr Geldman is currently in custody in the United States of America. The company has laid a complaint with the New Zealand Serious Fraud Office regarding Mr Geldman's actions," it said.

The statement said the company had tried to get overseas funding to safeguard investments but adverse publicity prompted that to collapse.

A liquidator has been appointed.

Complaints about the company arose last week with some investors reporting they had been told they would not be getting back any of the money they had invested.