Government agencies have apologised after system outages over the past four days that have seen travellers, pensioners and taxpayers affected by the failure of online services.

The collapse of the Department of Human Affairs' MyGov portal, which affected the ATO and other government sites, and Border Force's automated passport system followed a Telstra outage which left thousands of business unable to accept credit card and EFTPOS payments.

The latest bungle saw thousands of passengers delayed at Australia’s international airports after the automated e-gate passport checking system fell over on Monday morning leaving flights around the country delayed as queues grew around.

Five hours after the failure, the Australian Border Force (ABF) issued a terse statement apologising for the outage, giving no details on what had caused the passport system to go down.

“Our staff are working hard to minimise earlier delays caused by an outage” the ABF wrote. “All issues have now been rectified. We appreciate the patience of passengers at this time and apologise for any inconvenience this may have caused.”

Three days earlier, the federal Department of Human Services apologised for an outage that saw users locked out of the MyGov website on Friday, preventing thousands from submitting tax returns, updating social security details or reporting their income for benefits payments.

Department of Human Services General Manager Hank Jongen said Friday’s issues began around 9.40am with services being progressively restored after 12.30pm.

“We apologise for the inconvenience this outage undoubtedly caused for our customers. We understand the timing is unfortunate,” Jongen said.

“An investigation is underway to determine what caused the outage, but we have already ruled out any possibility of a cyber-attack.

“We can also confirm all regular payments were made overnight and were not impacted by this disruption.”

Along with the MyGov and Border Force disruptions, thousands of Australian businesses were unable to use their EFTPOS machines on Thursday following a Telstra outage.

Like the government agencies, Telstra apologised for the downtime with the company indicating network traffic was responsible.

“The outage occurred from approximately 2.30pm to 5.30pm on 11 July impacting some of Telstra’s IP network services, including EFTPOS, ATM and some payment platforms,” a spokesperson said.

“We are continuing to investigate the exact cause of this issues but early investigations suggest it was caused by an unusually large volume of traffic across network links in NSW.

"All services have now been restored. We’re really sorry for the impact and inconvenience to business and their customers.”