Trading halted at 11:30 a.m. and reopened for 30 minutes at the end of the day. Volume was down, with only 58 million New Zealand dollars (US$34 million) worth of shares changing hands, compared with an average day's turnover of NZ$80 million (US$47 million).
"The faults were due to a ... software upgrade. Today's closure was not the result of a failure of any technology," exchange spokeswoman Bridgit Vivian said in a statement.
Vivian said the glitch was not related to the Blaster worm virus, which has attacked some corporate networks and personal computers in recent days.
The problem also meant the exchange could not confirm share transfers were being properly recorded, she said.
About 150 companies are listed on the New Zealand market, which makes up just 0.1 percent of Morgan Stanley's MSCI World Index and less than 0.2 percent of total world share markets, by value. It has a total capitalization of NZ$47 billion (US$27.5 billion).