The fund continues to be focused on growth assets, says chief executive Adrian Orr.

The New Zealand Superannuation Fund has revealed a return of more than 20 per cent in a year, and appeared to take a swipe at the Government over the cost of investing in it.

On Thursday the fund announced that in the year to June 30 it made a return of 20.7 per cent, after expenses but before tax, raising the size of the fund to $35 billion. It followed a return of less than 2 per cent the previous year.

Chairwoman Catherine Savage said it was one of the fund's best annual performances, but the goal of the fund was long term returns.

"The fund is generating world class returns and creating significant wealth for New Zealanders on a sustained basis. It should not, however, be measured on its short-term returns. We are here to create long-term value for New Zealand taxpayers," Savage said in a statement.

READ MORE: Bill English slams NZ Super Fund for chief executive's 36 per cent pay increase

"The fund has now returned 10.2 per cent [a year], more than double the cost to the Government of contributing to it, over a period of nearly 14 years."

Savage was basing the claim on the returns on Treasury bills.

The statement could be seen as a swipe at National, which ceased contributions to the Super Fund when it took office in 2008 at a time when New Zealand was in recession and fiscal deficits loomed.

This means the Government has not made fresh contributions in nine of the 14 years since the fund was established.

Set up under the last Labour government and sometimes referred to as the "Cullen Fund", because of the influence former Finance Minister Michael Cullen had in its creation, the fund aims to help cover New Zealand's future pension liabilities.

Savage has clashed with the National-led government before.

In February it emerged that in 2016, the fund gave chief executive Adrian Orr a 36 per cent pay increase despite clear objections from then Finance Minister Bill English, the minister with responsibility for the fund.

When the issue became public, English, by then Prime Minister, appeared to warn the board could face not being reappointed.

"The Government has a view, the board's taken a different view - I think any board who takes a different view when it's 100 per cent subsidiary takes risks about tenure."

Labour has pledged to immediately resume payments to the NZ Super fund if it is elected, claiming the fund would be worth more than $50b if National had not halted contributions.

In a statement, Orr said the fund continued to be heavily weighted towards growth assets.

"A long investment horizon and low need for liquidity give us some unique advantages in the investment marketplace both in New Zealand and overseas. Our active investment strategies and strong weighting towards growth assets exploit these advantages in a disciplined and cost-conscious way."

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