The government's finances were in a healthy position before it rolled out a raft of emergency measures to support the economy because of the Covid-19 virus.
Official figures show a surplus of $1.39 billion for the eight months ended February a shade above expectations.
Tax revenue for the month was $187 million below forecast at $58.1 billion, with total revenue only $93m below forecast at $62.7bn.
Government expenses were $35m above forecast at $60.3bn.
"These results have reflected some of the Covid-19 related impacts, mainly in relation to the significant losses impacting the operating balance, total borrowings and assets and liabilities values," The Treasury said in a statement.
"The core Crown tax revenue and operating expenses have not been significantly impacted for these financial statements."
However, it noted the drop in interest rates and financial market volatility had increased losses on paper from investments and ACC liabilities.
The level of debt was below target at 19.2 percent of gross domestic product, just below expectations.
The government has since rolled out a $12.1 billion rescue package to support wages and companies cope with the virus, and increased its borrowing by $4bn for the rest of the financial year to end in June.