Reddit has launched a challenge in Australia's highest court against the nation's landmark social media ban for children.

The online forum is among 10 social media platforms which must bar Australians aged under 16 from having accounts, under a new law which began on Wednesday.

The ban, which is being watched closely around the world, was justified by campaigners and the government as necessary to protect children from harmful content and algorithms.

Reddit is complying with the ban, but in its case will argue that the policy has serious implications for privacy and political rights. It is the second such legal challenge, with two Australian teens also awaiting a High Court hearing.

"There are more effective ways for the Australian government to accomplish our shared goal of protecting youth," Reddit said in an update on its website.