Newscorp has bought a 7.5% stake in rival newspaper publisher Fairfax, for around $400 million.
Sky News business reporter Amber Higlett says the purchase raises the question of whether Newscorp plans a full takeover bid.
Fairfax has extensive interests in Australia and also owns most of New Zealand's daily newspapers, as well as internet auction site TradeMe.
The Newscorp raid follows the passing of new laws this week, that eased media ownership restrictions in Australia.