Embattled telco Optus is investigating another network outage that led to nine failed triple-0 calls made near Wollongong on the NSW south coast.

Optus has issued a statement saying the problem stemmed from a mobile phone tower site in Dapto.

It affected calls between 3am and 12:20pm on Sunday, including calls to the triple-0 network.

Optus says it had confirmed with police that "all callers who attempted to contact emergency services are OK".

According to Optus the triple-0 call failures included:

A caller who needed an ambulance and used another phone to contact emergency services.

A caller trying to call emergency services who could not get through.

Four calls referred to NSW Police to undertake welfare checks, including two from the same address (all confirmed as OK).

Two calle

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