Alarms were not raised despite five calls over the triple-zero outage, the Optus CEO has conceded. Photo: Dave Hunt/AAP PHOTOS

Optus was warned at least five times of a triple-zero call outage, as the telco giant's boss shuts down questions about whether he will resign over the scandal.

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A botched firewall update blocked hundreds of triple-zero calls from Optus customers in South Australia, Western Australia and the Northern Territory.

Early investigations appeared to show established processes were "not followed", Optus chief executive Stephen Rue said.

CEO Stephen Rue said calls

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