An investigation by the Australian telecommunications watchdog has found that TPG went almost eight hours before notifying Telstra about an outage affecting emergency service calls.

The Australian Communications and Media Authority (ACMA) found that the TPG network was down between 12.40am and 2am on August 15, which left most 4G customers unable to make voice calls, including emergency calls.

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

The ACMA said TPG became aware of the issue at 1.22am but did not report it to Telstra until 9.07am — breaching rules that specify telco carriers must contact Telstra “as soon as practicable” when they are 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.