After a week of horror for the telco, Optus has been forced to apologise for another outage which left customers unable to reach emergency services – the second such failure in less than two weeks.

The latest disruption occurred on Sunday between 3am and 12.20pm, affecting around 4500 customers in the Illawarra suburb of Dapto.

Nine triple-zero calls failed to connect during the blackout. The fault has been traced to one of the Singtel-owned company’s 9000 mobile phone towers.

One caller in need of an ambulance had to borrow another phone to reach paramedics, while another was unable to get through but has since been confirmed safe.

NSW Police carried out welfare checks on four others, with all found unharmed. Two additional calls were accidental.

An Optus spokesperson confirmed the incident and said an investigation was underway.

Optus chief executive Stephen Rue (pictured) admitted last week that staff failed to follow established upgrade procedures, calling the first outage a “human error” rather than a technical fault.

In the past week, Optus has seen Singtel chief executive Yuen Kuan Moon summoned for questioning, copped a $100 million fine for unconscionable sales, and scrapped its rebrand campaign in the midst of the crisis.

The latest outage comes just days after a catastrophic firewall upgrade failure crippled the network across four states, blocking hundreds of triple-zero calls and being linked to three deaths.

That fault is now the subject of a federal inquiry.

Fines and further regulatory action are on the table, with the Australian Communications and Media Authority already investigating whether Optus has adequately invested in its emergency service infrastructure.

NSW Opposition Leader Mark Speakman said Singtel must consider whether “those running the show are up to it”.

Communications Minister Anika Wells will meet with Optus executives and Singtel CEO Yuen Kuan Moon in Sydney this week.

Telstra also experienced an outage, today 29 September, in Western Australia’s South West, affecting 4G services and disrupting access to triple-zero calls.