Peng Shuai is at the centre of growing concern after the tennis star alleged earlier this month that a powerful Chinese politician sexually assaulted her.

The 35-year-old Peng, a former world number one in doubles, has not been seen since.

It was the first time that the #MeToo movement has struck at the top echelons of China's ruling Communist Party.

Here's what we know so far:

On November 2, Peng appears to have posted on China's Twitter-like Weibo damaging claims about former vice-premier Zhang Gaoli. Peng alleged that he had coerced her into sex during a long-time on-off relationship.

There has been no response from Zhang, who is in his seventies.

Peng's post was soon deleted, but not before social media users took screenshots. Those were censored on China's heavily vetted Internet and still are.

But Peng's allegation was posted to Twitter -- which is banned in China -- allowing it to reach a worldwide audience.

Peng still comes up on search results online in China, but her allegations do not, and searches for her and Zhang together also show nothing.

On Twitter, #WhereIsPengShuai began to gain traction, with tennis players past and present using the hashtag to voice concern for her safety.

Peng Shuai is a former world number one in doubles Peng Shuai is a former world number one in doubles Photo: AFP / William WEST

Four-time Grand Slam champion Naomi Osaka wrote that she was "in shock", with tennis great Serena Williams stating she was "devastated and shocked" and calling for an investigation.

Men's world number one Novak Djokovic told reporters: "Honestly, it's shocking that she's missing."

The Women's Tennis Association (WTA) called for Peng's allegations to "be investigated fully, fairly, transparently and without censorship".

WTA chairman Steve Simon said he had been told "from several sources" that Peng was safe.

China's tennis association did not reply to AFP requests for comment and the foreign ministry also declined to comment.

As the outcry grew over Peng's case, White House spokesperson Jen Psaki said the Biden administration wanted China to "provide independent, verifiable proof" of Peng's whereabouts.

Meanwhile, the United Nations also weighed in, insisting on a fully transparent investigation into her claims.

There was a new twist when China's state-run CGTN published a screenshot on Twitter of an email it alleged was from Peng to the WTA in which she claimed her accusations were "not true" and "everything is fine".

Doubts were quickly flagged about the awkward language and a cursor visible in the screenshot. Simon said it "only raises my concerns".

Late Friday, four undated photographs -- which could not be independently verified by AFP -- were shared by the Twitter account @shen_shiwei, labelled by the social media giant as "Chinese state-affiliated media".