The ASX equity market paused trading this morning, and will not open until tomorrow morning.
The market will not open again until 10am tomorrow as the ASX works to fix the issue.
Today was the go-live for the refreshed ASX Trade system, which is the trading platform for ASX's equity market.
The issue was identified by the ASX and its technology partner Nasdaq as a software issue limited to the trading of multiple securities in a single order creating inaccurate market data.
The ASX said the issue would be resolved over night and that the market would be able to open again at 10am.
"The outage falls short of the high standards we set ourselves and the standards others expect of us," ASX chief executive and managing director Dominic Stevens said.
"Notwithstanding the extensive testing and rehearsals, and the involvement of our technology provider, ASX accepts responsibility. The obligation to get this right and provide a reliable and resilient trading system for the market rests with us."
"While I am disappointed with today's outage, we are determined to continue our program of contemporising ASX's technology stack from top to bottom. This initiative is critical to ASX building an exchange for the future and ensuring we best serve the needs of our customers and the Australian market."
Earlier in the day, the stock exchange said it was aware of a market data issue impacting partition-three securities. The market paused trading just before 10.30am today.
ASX listed securities are divided into four partitions each representing about a quarter of the market. Partition three which the ASX says has caused the halt includes energy, industrial, index and securities whose classification is pending.
However, if one partition fails to trade due to an error, ASX halts trading of all four. This is in part due to difficulty in calculating market indices and other securities whose price depends on other securities.
ASX, over the weekend, was slated for migration for the ASX Trade Refresh that started in August 2019 and had a go-live of today. The refresh project was for three interfaces the ASX Trade: ITCH, OUCH and OI.
About $6 billion was traded on the ASX's cash market daily on an average in October, cross about 1.4 million trades. Of this $5.2 billion was on-market.