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Natural Dairy's bid to buy the Crafar family farms is "extremely complex," Land Information Minister Maurice Williamson said today.

The Overseas Investment Office (OIO) is considering Hong Kong-based Natural Dairy's bid for the 20 central and lower North Island farms.

However, the complex nature of the bid meant the OIO could not be specific about when it would give its recommendation, Mr Williamson said.

The Government would make a final decision once it had the OIO's recommendation.

The Overseas Investment Office told last week it was "highly unlikely" it would be able to complete its assessment within its 50 working day guideline.

The Hong-Kong backed Natural Dairy application for the farms was lodged with the Overseas Investment Office on July 7, and the preliminary assessment was completed on July 16, taking the deadline to the end of this week.

But an OIO spokesperson said last week it was doubtful the office would be able to complete its assessment within the timeframe because of the complex nature of the case.

"We can't be more specific in terms of the timeframe when we will complete the application because it is a very complex application, " the office said.

The office earlier sent back Natural Dairy's application saying it required more information about its proposed New Zealand acquisitions.

It was three months before Natural Dairy resubmitted its application.