The severity of the financial crisis has seen the Government Superannuation Fund report an after-tax deficit of $583.3 million for the year to June.
The previous year, the retirement scheme for public servants recorded a deficit of nearly $261 million.
The result represents a 16.8% loss of return on the fund's assets, compared to an average return of 0.7% over the past five years.
The fund's chief executive, Alan Langford, says its losses are comparable to those of other large, long-term funds.
He says the market does appear to have turned, and there have been positive results in July and August; he is cautious, however, about what the rest of the year will bring.
Asset value has plunged nearly $1 billion
About half of the fund is invested in international shares, a quarter in fixed-interest investments, 10% in New Zealand shares and the rest in property and commodities.
Closed to new members in 1992, the scheme currently has some 72,000 members, made up of nearly 24,000 contributors and 48,000 people receiving annuities.
Its assets, which have plunged in value from $3.5 billion to $2.65 billion, are insufficient to cover its commitments; any annual shortfall in the cost of entitlements is topped up by the government each year.