International concern continues to grow for Chinese tennis star Peng Shuai, who has not been seen in public since making explosive against a top Communist Party official.

Peng, 35, one of China's most recognizable athletes, accused former Vice Premier Zhang Gaoli of coercing her into sex, according to screenshots of a since-deleted social media post dated November 2.

Chinese censors have wiped out any mention of the accusation online and blocked her social media accounts on China's internet. An email purportedly from Peng but released by Chinese state media has only over her whereabouts.

Some of the sport's biggest names have called on China to confirm her safety and investigate her allegations. Women's Tennis Association (WTA) Chairman and CEO Steve Simon has if Peng is not accounted for and her accusations not properly investigated.

Here's what you need to know about the accusation -- and the evolving fallout.

WHO IS PENG SHUAI?

Peng is a two-time Grand Slam doubles champion and one of China's top tennis players.

From Hunan, in central China, the 35-year-old made history in 2014 when she became the first Chinese player -- male or female -- to achieve the world No.1 doubles ranking.

Her two major doubles titles were won at Wimbledon in 2013 and the French Open in 2014. Peng also at the 2014 US Open, and is a three-time Olympian. She's won 25 tour titles and obtained a No. 17 world singles rank.

The international success of Peng and fellow Chinese tennis stars Li Na and Zheng Jie, has been credited with helping the sport's popularity soar in China, particularly for the women's game.

WHO IS ZHANG GAOLI AND WHAT ACCUSATIONS HAS PENG LEVELLED?

Zhang Gaoli, 75, served on the ruling Communist Party's seven-person Politiburo Standing Committee -- the country's supreme leadership body -- from 2012 to 2017 during Chinese leader Xi Jinping's first term in power. He retired as vice premier in 2018.

In a since-deleted social media post dated November 2, Peng accused Zhang of coercing her into sex and alleges a relationship over an intermittent period that spanned at least 10 years.

About three years ago, after Zhang had retired, the post alleges Peng was invited by him to play tennis in Beijing. Afterward, she wrote, Zhang and his wife brought Peng to their home, where Peng claimed she was pressured into having sex with Zhang.

"That afternoon I did not agree at first and was crying all the time," Peng wrote. After dinner with Zhang and his wife, and following much persuading from Zhang, she relented, according to the post.

"Why did you have to come back to me, took me to your home to force me to have sex with you?" she wrote.

"I couldn't describe how disgusted I was, and how many times I asked myself am I still a human? I feel like a walking corpse. Every day I was acting, which person is the real me?"

Peng said she did not have evidence to prove her allegations, and claimed Zhang was always worried that she would record things.

CNN cannot independently verify the authenticity of the more than 1,600-word post.

WHAT HAS HAPPENED TO HER?

Peng's explosive allegation prompted China's censors to respond at an unprecedented level.

Her post on Weibo, China's Twitter-like platform, was deleted within 30 minutes of publication, and censors scrubbed any mention of the accusation online. Her Weibo account, which has more than half a million followers, is still blocked from searchers on the platform.

Peng has not been seen in public since the accusation and her whereabouts have not been publicly disclosed.

CNN has repeatedly reached out for comment to both her and China's State Council, which handles press inquires for the central government.

WTA chief Simon told CNN he had been in conversation with counterparts at the Chinese Tennis Association, who had provided assurances Peng was unharmed in Beijing. However, attempts to reach Peng directly had proved unsuccessful, he said.

WHAT HAVE AUTHORITIES SAID?

Chinese authorities have so far refused to publicly acknowledge Peng's allegations against Zhang.

Chinese Ministry of Foreign Affairs spokesperson Zhao Lijian said in separate comments on November 17 and 18 the issue "wasn't a diplomatic matter," and declined to comment further to reporters.

But on November 17, Chinese state media released an email, purportedly sent to WTA's Simon from Peng, walking back her allegations and claiming she is fine.

Simon cast doubt on the email's veracity, describing it as a "staged statement of some type." He has demanded China provide "independent and verifiable proof" Peng is safe.

"Whether she was coerced into writing it, someone wrote it for her, we don't know," he said. "But at this point I don't think there's any validity in it and we won't be comfortable until we have a chance to speak with her," he added.

The International Olympic Committee (IOC) has said it wouldn't comment on the matter and suggested "quiet diplomacy" should be approached, according to Reuters.

Peng's disappearance has sparked a wave of concern, with some of the world's top tennis players speaking out using the hashtag #WhereIsPengShuai.

Naomi Osaka, Serena Williams, Novak Djokovic, Billie Jean King and Chris Evert are among those expressing shock and calling for her allegations to be investigated.

WHAT HAPPENS NEXT?

There is significant pressure on Chinese authorities to provide proof Peng is safe. WTA chief Simon said he is willing to lose hundreds of millions of dollars worth of business in China if she is not fully accounted for.

"We're definitely willing to pull our business and deal with all the complications that come with it," Simon said in an interview on November 18 with CNN. "Because this is certainly, this is bigger than the business," he added.

And tennis in China is big business, with the WTA commitments alone amounting to . The WTA also has its Asia-Pacific headquarters based in Beijing and the WTA has a 10-year deal with China to host the WTA Finals in the southern Chinese city of Shenzhen.

The controversy could also impact the upcoming 2022 Beijing Winter Olympics, which kick off on February 4.

The WTA has been more forceful than other organizations that have previously collided with Chinese authorities over issues of free speech and human rights. Sports stars or companies that speak out have been met with significant public and political backlash, as well as loss of access.

Natasha Kassam, director of public opinion and foreign policy at the Lowy Institute, said the WTA has some leverage over China.

"Most of the other cases where we've seen China interfering with sporting organizations, they haven't had a colleague or a teammate disappear. This is on a different level. So the WTA's reaction is strong, and it's helpful, and it's using the leverage that it has."