A "connectivity issue" saw traffic halted shortly after the 10am open, paralysing one of Asia-Pacific's major markets and forcing 6,700 initial trades to be reviewed, the bourse said.

"The markets were halted at 10:05am when ASX detected a connectivity issue. ASX has worked with its technology vendor to resolve the issue," it said.

The Sydney exchange has a total market capitalisation of approximately Aus$1.2 trillion (US$1.26 trillion) and is ranked the eighth-largest market in the world in terms of free market capitalisation, according to its website.

Approximately US$5 billion changes hands daily on the ASX.

The early trades were ultimately approved and the market opened at 2:00pm for a brief two-hour session, surging 1.87 percent in the first half-hour after European Union leaders sealed a major deal to resolve the region's debt woes.

The benchmark S&P/ASX 200 index had initially fallen 0.3 points to 4,242.2 before the glitch was detected.

It is the second time this year technical issues have hit the exchange, with a similar glitch during the afternoon session on February 28 lasting just over an hour.

The index had closed 0.35 percent higher at 4,242.5 on Wednesday, reversing a Europe-linked dip after domestic inflation came in lower than expected, fuelling hopes of an interest rate cut.

Dealers had expected to open stronger after a rally on Wall Street, spurred by investors feeling more confident about European leaders finding a solution to their debt crisis.

"Traders will be encouraged by the agreement to recapitalise the banks," Stan Shamu of IG markets said.

Analysts feared a significant problem as the outage entered its second hour and said a full-day halt would be devastating given the likely boost that had been expected from the European summit and some strong local earnings results.

"There is a big concern because we have been down for so long, meaning there could be a major issue here," said Michael McCarthy, CMC Markets chief market strategist.