Optus has apologised for a second triple-zero outage in as many weeks, as local executives prepare for showdown talks with the embattled telco's owners.

The latest issue is linked to a mobile phone tower in NSW that affected 4500 users in the Dapto area on Sunday between 3am and 12.20pm.

A review by the telco has identified nine failed calls to triple zero, but Optus says those affected "are OK" and the issue has been rectified.

One of those callers required an ambulance and used another phone to contact emergency services.

Another was trying to call emergency services but couldn't get through and had made accidental calls.

The failure is the second time in less than a fortnight a major Optus outage has prevented people accessing emergency services.

Finance Minister Katy Gallagher de

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