Pressure is rising on Optus to be penalised as investigations are promised into an outage linked to at least four deaths.

A botched firewall update at 12.30am on Thursday blocked hundreds of calls to triple zero in South Australia, Western Australia and the Northern Territory.

An eight-week-old boy and a 68-year-old woman died in Adelaide during the fault, along with a 74-year-old man and 49-year-old in Perth.

Optus was unaware of the outage for triple zero calls until being notified by a customer about 1.30pm, Optus chief executive Stephen Rue said.

The update was cancelled and access to the emergency line was restored after 13 hours.

Mr Rue admitted Optus had been contacted by the telecommunications industry ombudsman about two complaints of people trying to inform the company about

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