Optus chief executive Kelly Bayer Rosmarin says a national outage of phone and internet services that disrupted 10 million customers, shut down Melbourne’s trains, and stopped some people making calls to emergency services was too “technical” to explain.

Ms Bayer Rosmarin told The Australian Financial Review that a “technical network fault” caused the outage but would not specify what exactly it was, or where or how it occurred, after the Singaporean-owned company restored all services by late afternoon on Wednesday.