BEIJING, March 4-- Thousands of Chinese viewers illegally downloaded the new season of "House of Cards" after streaming site Sohu failed to release the American political drama when Netflix rolled out all 13 episodes in late February.

Entertainment magazine Variety cited piracy-tracking firm Excipio as saying China was the largest source of illicit downloads in the first 24 hours after the episodes hit torrent sites. According to the report, the show was downloaded to 60,538 unique devices in China within a day of becoming available.

Research firm GlobalWebIndex estimated that more than 20 million Chinese used virtual private network services to access Netflix, which is currently not available in China.

Though China has strengthened its efforts to crack down on piracy in recent years, culminating in shutting down two major subtitle-sharing websites, Internet users still managed to find ways to download content not available in China.

On Chinese social networking site Sina Weibo, users have posted messages containing torrent sharing files, most of which were stored by Dropbox-like online file hosting services.

Industry insiders say this may deal a blow to streaming sites, which over the years have spent millions of dollars buying the rights to foreign TV and movie productions.

According to a regulation released by China's media watchdog last September, video streaming sites must obtain publication licenses for imported films and TV series they want to host. The administration also asked streaming sites to register all foreign films and TV series they plan to offer to media administrative departments by March 31.

As a result, it will be difficult for streaming sites to show new American TV series in China as they are released in the United States. Audiences will only be able to watch the show after the whole season has been released and passes review.

It is yet to be seen whether more foreign TV series will be affected by the regulation, but many streaming sites have tried re-launching older series such as "Prison Break" and "Heroes."