China is now Skype's biggest market, despite legal issues that may make parts of the internet telephone service illegal in the country. 

EBay, which acquired Skype in September last year, said yesterday that there are 13 million registered Skype users in China, about 13 per cent of the total, and more than in any other nation. 

The Skype user numbers were released as part of eBay's Analyst Day (PDF download) presentation. 

After China, the next largest nation for Skype is the US which has fewer than half the Chinese total at about six million. The company claims more than 100 million users worldwide.

However, the SkypeOut service, which lets users call traditional telephone numbers at low cost, appears to be of uncertain legality in China.

According to media reports last year, at least one local telecoms operator in China has suggested that a 2004 regulation forbids SkypeOut and similar services.

Only a small number of licensed telecoms operators are able to offer such services, other reports say, and Skype does not have a licence.

Chinese telecoms licenses are traditionally difficult to obtain, particularly for foreign-controlled companies.