An independent investigation is being launched into the way Overseas Investment Office (OIO) carried out its good character test over the sale of a Taranaki farm to two Argentine brothers.

Land Information Minister Louise Upston said this morning she had "some concerns" over how the OIO carried out the good test, which it uses as it considers whether to give consent for a land purchase by overseas buyers.

Photo: SUPPLIED

Documents obtained by the Labour Party show Rafael and Federico Grozovsky - who bought Onetai Station in 2014 - were found criminally responsible for chemical dumping from their Buenos Aires tannery.

The OIO last week said it was satisfied due process was followed when it granted consent for the pair to buy the 1300ha farm near Awakino, but shortly after said it was investigating issues raised in media reports.

The brothers are linked with Panamanian law firm Mossack Fonseca, which is at the centre of the Panama Papers revelations about how the rich hide their wealth in overseas trusts.

Ms Upston said an investigation was triggered on Friday when the serious allegations about the brothers' pollution convictions were made public.

"I do have some concerns about the process that the office have used around the good character test so I have asked that a review be undertaken about that."

The review announced today will cover this instance, and look at how the office performs good character tests in general.

Asked whether the OIO was aware of the toxic spill and the brothers' convictions, Ms Upston said it was aware of "some information".

Ms Upston said the office was aware of a connection between the company which bought the farm and a "shared office" with Mossack Fonseca.

Labour Party's finance spokesperson Grant Robertson said the review was well overdue.

"Nearly 99 percent of the applications that have come before the Overseas Investment Office in recent years have been accepted. That indicates there is a very weak process in place.