Australia's online safety watchdog said Thursday it was being taken to court by Elon Musk's X in a fight over the platform's failure to outline how it combats child sexual abuse content.

Last month, eSafety commissioner Julie Inman Grant slapped an Aus$610,500 (US$388,000) fine on the company formerly known as Twitter for failing to respond to questions sent in February about how it is tackling the issue on its platform.

The social media giant missed an extended mid-November deadline to pay the fine, the eSafety commission said this week, adding that it was "considering further steps".

Instead, X has taken the case to Australia's federal court.

"X Corp. has lodged proceedings seeking judicial review of decisions of the eSafety Commissioner in this matter," an eSafety commission spokesperson told AFP.

"ESafety continues to consider its options in relation to X Corp's non-compliance with the reporting notice but cannot comment on legal proceedings."

Documents have been filed with the federal court in Melbourne, and AFP has sought comment from lawyers acting for X in Australia.

When contacted by AFP, X responded with an automatic email: "Busy now, please check back later".

Inman Grant -- herself a former Twitter employee -- last month urged X to show it was taking "tangible action" to clean up the platform.

"Twitter/X has stated publicly that tackling child sexual exploitation is the number one priority for the company, but it can't just be empty talk," she said at the time.

Billionaire Musk has cut more than 80 percent of X's global workforce since his takeover in October 2022, including many of the content moderators responsible for stamping out abusive content.

Proactive detection of child sexual exploitation on X fell from 90 percent to 75 percent in the three months after the takeover, Inman Grant said.

Australia has spearheaded the global drive to regulate social media platforms, and this is not the first time Inman Grant has singled out X or Musk.

In June, she raised concerns about a spike in more general "toxicity and hate" following Musk's takeover of the platform.