Australia's former leader on Wednesday defended secret arrangements he made to swear himself in to key portfolios including defence and treasury, saying he would only have used the roles in an emergency during the Covid-19 pandemic.

Revelations about Scott Morrison's covert actions -- labelled by his successor as the creation of a "shadow government" -- have sparked a political firestorm in Australia this week.

During a lengthy and at-times fiery press conference Wednesday, Morrison rejected calls that he resign from parliament, including those from his own home affairs minister.

"You're standing on the shore after the fact. I was steering the ship in the middle of the Tempest," he said.

He faced a barrage of questions about why he failed to tell the public -- or even many of his fellow ministers -- that he was giving himself the additional powers.

The conservative former prime minister added that he gained "no personal advantage" from being sworn in to administer five portfolios and stressed that the arrangements were only to be used in an emergency, such as if a minister died during the pandemic.

Morrison said he only used the powers once, which was to override his resources minister and block a controversial offshore gas project -- a move he conceded was separate from the pandemic.

"I'm very happy with that decision," he said.

"And if people think I should have made a different decision and allowed that project to proceed... well they can make that argument."

During his time in power, Morrison was routinely criticised for a lack of transparency -- an indictment that burst onto the global stage when French President Emmanuel Macron accused him of lying over an abandoned submarine deal.

Morrison's conservative coalition lost power in May elections, ending nearly a decade of centre-right rule in the country.

In Australia, elected politicians are selected by the prime minister before being sworn in by the governor-general in a formal ceremony that is usually publicly recorded.

As yet, it is not clear whether Morrison will face any political or legal fallout from the scandal.

Australia's new prime minister, Anthony Albanese, has asked the solicitor-general to advise on whether his predecessor acted legally.

He said Morrison's actions were "fundamentally a trashing of our democratic system".