The Australian Communications and Media Authority (ACMA) discovered that the TPG network was down from 12.40am to 2am on August 15, leaving most 4G customers unable to make voice calls, including those to emergency services.

Most triple-zero calls made during the outage went through because they hitched onto other networks.

The ACMA indicated that TPG was aware of the issue at 1.22am but failed to report it to Telstra until 9.07am, violating rules that require telecommunications carriers to inform Telstra “as soon as practicable” upon becoming aware of a disruption to emergency service calls.

“It’s crucial that all telcos have their systems and processes in place to ensure any network outages impacting Triple Zero are identified and addressed as soon as possible,” ACMA member Samantha Yorke said in a statement.

“They must also take timely action to alert other key stakeholders in the Triple Zero ecosystem where a problem is being experienced.”

The investigation found no customers suffered any harm as a result of the company’s failure to comply with the rules.

ACMA has issued a formal warning to TPG over the incident.

TPG has advised that the cause of the breach was a result of human error, and all relevant staff have been trained.

“TPG Telecom takes its regulatory responsibilities seriously and has implemented improved processes and training to prevent this happening again,” a spokesperson said.

The ACMA said it is cracking down on compliance around emergency call services.