Tom Online now has at least 23.5 million registered users in China, and these figures almost certainly underestimate the true size of the audience.
The figures suggest that almost one in five Skype users is Chinese. Skype claims 136 million registered users worldwide.
The rapid increase comes despite the censorship of text messages, and questions about the legality of some of Skype's VoIP services in China, which have prevented Tom Online from offering the Skype Out service.
Wang Lei Lei, chief executive at Tom Online, revealed the dramatic acceleration of Skype's Chinese audience in a conference call with analysts to discuss the Chinese company's third-quarter results.
The disclosure almost certainly does not reveal the full extent of Skype's popularity in China, because some users have signed up through overseas Skype websites, instead of using the Tom Online Skype site.
Chinese telecoms regulations prevent Tom Online from offering Skype Out in its version of the software, prompting some subscribers to bypass it.
Tom Online has also blocked politically sensitive phrases in Chinese text messages to avoid upsetting the Chinese government. The two companies operate a joint venture in China which is 51 per cent owned by Tom Online.
"During this quarter we have begun to see our Tom-Skype user base grow at a much faster pace as we have optimised our marketing programme," said Wang.
"But more importantly we believe that the Tom-Skype community is beginning to reach critical mass and achieve a positive network effect.
"At the end of October we had 23.5 million Tom-Skype registered users, an increase of more than eight million from the end of July."
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