Reports of child grooming and vile content on popular game service Roblox has “alarmed” the communications minister, Anika Wells, who has demanded the platform explain how it is addressing sexual and self-harm material, and that its PG rating be examined by the Australian Classification Board.

The eSafety Commissioner has also written to the game platform, saying it plans to test the promises it made about keeping children safe online, including disabling chat features and making underage accounts private.

“We remain highly concerned by ongoing reports regarding the exploitation of children on the Roblox service, and exposure to harmful material,” the eSafety commissioner, Julie Inman Grant, said.

Roblox has come under scrutiny after reports that children can be exposed to inappropriate content on the platform, which allows users to create their own mini-games inside the system.

Guardian Australia published a report last November documenting a week of virtual sexual harassment and violence. While playing as an eight-year-old girl, the reporter was given a sexualised avatar, cyberbullied, aggressively killed, sexually assaulted and shat on – all with parental control settings in place.

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While platforms like Instagram, Snapchat, YouTube and Kick were included in Australia’s under-16s social media ban, gaming sites like Roblox were not.

Wells and her department were investigating other levers to regulate services like Roblox.

The minister has written to Roblox requesting an urgent meeting, saying she was “alarmed by reports of children being exposed to graphic and gratuitous user-generated content on the platform, including sexually explicit and suicidal material”.

“Even more disturbing are ongoing reports and concerns about children being approached and groomed by predators, who actively seek to exploit their curiosity and innocence,” she said in the letter.

Guardian Australia understands Roblox has not yet responded to the letter.

In her letter, Wells pointed to media reports alleging children can access spaces on the game meant for adults which include explicit sexual content, and charges laid against a Queensland man accused of grooming hundreds of children on platforms like Roblox, Fortnite and Snapchat.

Wells has also asked the eSafety Commissioner about any short-term measures that could be taken, and separately has written to the Classification Board to ask if Roblox’s PG rating remains appropriate.

In the letter to Roblox, Wells noted the company had worked with the eSafety Commissioner on additional safety measures for children, but that issues appeared to continue.

“This is untenable, and these issues are of deep concern to many Australians parents and carers,” she wrote, saying she was keen to hear what Roblox was doing to prevent adults contacting children, and to protect children from inappropriate experiences.

The eSafety office said it had also written to Roblox last week, saying it planned to test how the platform was complying with commitments like making under-16s private by default, new tools to prevent adult users from contacting children, and restricting chat features. After that testing, eSafety foreshadowed it “may take further action under the Online Safety Act”.

“I welcome the Minister for Communications’ correspondence and the Australian Government’s support on this important issue, as we use all of the tools available to us to keep Australian kids safe online,” Inman Grant said.