The issue was triggered after aerial fibre line was damaged by vandals attempting to steal copper, impacting customers in the Frankston and Mornington Peninsula areas, southeast of Melbourne.
All 14,546 services impacted have been restored, according to the Optus website.
The embattled telco had earlier warned that emergency services were affected, telling customers they could only call triple zero if they were within range of another mobile network or had access to wi-fi.
Optus spokeswoman Jane McNamara said the telco believed no triple-zero calls were disrupted.
She said the incident was frustrating, adding that criminals had cut the fibre which provided vital connectivity to customers.
"Our technicians have been on site since early this morning. We do have that photo evidence and it's clear that there had been a cut made," she told ABC Radio.
"We know copper has been removed from the pit and we have contacted police."
The failure is the fourth time in months a major Optus outage has prevented people accessing emergency services.
A scheduled firewall upgrade in South Australia triggered a communications outage on September 18 linked to the deaths of three Australians.
Normal calls were largely unaffected, but the outage blocked about 600 triple-zero calls from connecting to emergency services.
Premier Jacinta Allan earlier said she was seeking urgent advice on the situation.
"There are too many people out in the community experiencing an outage that may be impacting their ability to contact emergency services," she told reporters on Wednesday.
"I can understand why there is a great concern in the community, particularly given some of the more recent incidents that have involved Optus."
Optus is the subject of a Senate inquiry following the September outage, which will examine the regulator's response and whether more could have been done by authorities or the government to prevent the loss of life.
Inquiry chairwoman Senator Sarah Hanson-Young called for an urgent review of Optus' licence.
"They are clearly not capable of providing this essential service and keeping Australians safe," she said.
Opposition communications spokeswoman Melissa McIntosh said the outage was unacceptable, regardless of the fault.
"Optus has an obligation to provide triple-zero services to Australians anywhere and at any time. The ongoing triple-zero outages must stop," she said in a statement.
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