SYDNEY: Australia said on Thursday it would investigate an outage at telco Optus that cut off internet and phone connections to nearly half of its population, causing widespread chaos and leading some small business customers to seek compensation.

More than 10 million Australians, 40% of the population, were hit by the 12-hour network blackout at the nation's No. 2 telco firm for much of Wednesday, triggering fury and frustration among customers and raising concerns about the country's telecommunications infrastructure.

The government would undertake a post-incident review into the outage that hit payments, transport and hospitals, Communications Minister Michelle Rowland said, describing the impacts as "particularly concerning."

"While we welcome that Optus services were restored over the course of the day, it is critical the government conducts a process to identify lessons to be learned from yesterday's outage," Rowland said in a statement.

Australia's media regulator will conduct a separate review into the outage after emergency triple zero ("000") calls went down on Optus landlines, Rowland added.

Taxi driver Ian Martin-Brown told Nine Network that he might take legal action after losing a day's work. Other customers including cafe owners and niche online retailers told media outlets they would seek compensation for lost revenue.

"There's no doubt that it has to be on the table," Assistant Treasurer Stephen Jones told ABC Radio. "If you're a small business that's lost a day's takings because your phone system wasn't working then you're going to be asking those hard questions."

Optus, owned by Singapore Telecommunications (Singtel) (STEL.SI), did not immediately respond to a request for comment.

Optus has not given the cause for the unprecedented outage, one of the biggest the country has witnessed, but it has ruled out for now any cyber hacks.

Singtel said the outage had "let down our customers" and apologised as it reported on Thursday an 83% jump in half-yearly profit.

But UBS analysts said Optus now faces the possibility of losing customers to Telstra (TLS.AX), the nation's largest telco firm, and TPG Telecom (TPG.AX) due to "strong brand perceptions" of the network quality of rivals.

The government said it would also check the possibility of allowing customers to switch to available networks when future outages occur.

"The industry is prepared to be involved ... it is feasible and we're going to take this forward as a government," Rowland told the ABC.