Another major government IT outlet has failed, with the ATO site going down at its busiest time.

A tech failure knocked out the Australian Taxation Office’s online customer services this week from early Wednesday afternoon until after 8pm, although the main webpage remained operational.

The outage came just hours after Tax Commissioner Chris Jordan announced the annual tax season was under way without any system failures, in an address at Canberra's National Press Club.

At the time, he said about 210,000 tax returns from individuals and agents had already been lodged online.

“While we believe we have done everything we can and expect things to go smoothly, we are ready to respond quickly if there are any hiccups or unexpected outages,” he said. 

“These outages were highly unusual and were disruptive for the users of our systems, particularly the tax profession, the superannuation and software industries."”

The crash has been likened to the infamous #CensusFail of 2016, with some accusing the ATO of being too reliant on contractors. 

The latest shutdown follows a larger collapse of ATO's website and internal systems last year, big rebuilding efforts earlier this year, and its EOFY failure of 2015. 

The ATO issued a statement saying no data had been lost and systems were not compromised.

“We identified intermittent system issues early this afternoon affecting our mainframe and impacting on our services to the community. This was caused by applications running incorrectly,” it said.

“We took controlled action to reboot our mainframe and resolve this issue. We then brought our services back online methodically to ensure system availability and stability.

“While an outage is not optimal, our decision today to address our degraded system performance was to ensure they were fully operational for the 8.00-9.00pm window when we know the majority of people choose to lodge their tax returns.”