Telstra chief executive Vicki Brady apologises to the company's customers, saying the telco let them down and that investigations into the cause of Wednesday's Telstra outage are continuing.

The absent Telstra CEO is expected to face intense scrutiny when she returns to the country following the telco’s nationwide outages.

Telstra boss Vicki Brady has apologised for this week’s mass outage, as Communications Minister Anika Wells vowed the government would hold the telco to account.