The Women's Tennis Association is prepared to pull its tournaments out of China if they are not satisfied with the response to the sexual assault allegation made by former doubles world number one Peng Shuai, chief executive Steve Simon has told US media.

Peng has not been seen in public since she accused a former vice-premier of China, Zhang Gaoli, of sexual assault in a social media post that was deleted half an hour later.

Neither Zhang or the Chinese government have commented on Peng's allegation and discussion of the topic has been blocked on China's heavily censored internet.

Concern among the global tennis community and beyond has grown over Peng's safety and whereabouts since her allegation, with the WTA calling for an investigation and the world's top players tweeting #WhereIsPengShuai.

Simon upped the ante considerably on Thursday when he told various US media outlets that the tour would consider pulling tournaments worth tens of millions of dollars out of China.

"We're definitely willing to pull our business and deal with all the complications that come with it," Simon told CNN in an interview.

"Because this is certainly, this is bigger than the business. Women need to be respected and not censored."

China has been the focus of aggressive WTA expansion over the last decade and hosted nine tournaments in the 2019 season - the last before the disruption caused by the Covid-19 pandemic - with a total $30.4 million prize money on offer.

Simon on Wednesday cast doubt on the authenticity of an e-mail purportedly from Peng and leaked to a Chinese state media outlet, in which the 35-year-old player was said to deny the sexual assault allegations.

Women's tennis greats Serena Williams and Billie Jean King on Thursday added their voices to the growing chorus of tennis players and other sporting figures calling for an independent investigation.

"This must be investigated and we must not stay silent," American Williams wrote on social media. "Sending love to her and her family during this incredibly difficult time."

The Professional Tennis Players Association (PTPA), a new body representing players set up by men's world number one Novak Djokovic and Vasek Pospisil, said players must be prepared to take action if Peng's safety cannot be confirmed.

"The PTPA is advocating for independent evidence confirming the safety and location of WTA player, Peng Shuai," the body said in statement.

"We must unite and be willing to take action unless corroborated evidence is provided to the world about Peng's wellbeing."