update Westpac technical staff have worked through the night to restore critical EFTPOS and ATM facilities after a server crash froze the bank in its tracks.
Westpac officially reported the outage to its customers last night at around 9pm AEST.
"We're experiencing server problems at present and some payments aren't being processed," Westpac told its customers via Twitter.
That outage meant that Westpac customers were unable to withdraw cash from the bank's network of ATMs, while Westpac merchants were left without a way to process card payments.
"Our ATM and some merchant systems are down. We're working very hard to get our systems back up as soon as possible.
"Phone banking is also working, but if you're trying to contact an operator then please note we're getting very high volumes," the bank later added.
Customers were able to withdraw cash from major supermarkets Coles and Woolworths, however.
The bank assured that systems were back up and running this morning.
Westpac's last outage came in May, when an air-conditioning failure in the bank's primary datacentre forced the bank to take services offline to prevent further damage to system infrastructure due to overheating.
"We did take the decision to focus on restoring services from the impacted datacentre rather than switch to our backup systems, as it would have taken more time to do so," said Paul Marriage, head of media relations for Westpac, said at the time.
Westpac told ZDNet Australia this morning that the latest outage was minor and had nothing to do with its datacentre.
One of Westpac's major merchant customers, RailCorp, was affected by both outages, meaning that commuters were forced to pay cash for tickets until the system hiccup had been resolved.
"EFTPOS facilities down at Sydney Domestic Terminal train station. Don't expect any sympathy from the staff — bring cash #fail," one Twitter user noted last night.
After the last outage, RailCorp said it would hold talks with Westpac to discuss downtime in light of its contract requirements.
Updated at 10:11am, 9 September 2011: added comment from Westpac