BEIJING — Chinese regulators have ordered streaming-video websites nationwide to take down four popular American television series, “The Big Bang Theory,” “The Good Wife,” “NCIS” and “The Practice.”

The move precedes new rules seeking to close a loophole that has allowed foreign shows to flourish online, even as censors have limited them on broadcast television.

Unlike previous takedown orders, this one gave no explanation from China’s top broadcast regulator, the State Administration of Press, Publication, Radio, Film and Television, employees of two online streaming sites said Sunday. The order was issued Friday, one employee said.

In recent years, shows like AMC’s “The Walking Dead,” the CW’s “The Vampire Diaries” and Netflix’s “House of Cards” have found avid online audiences in China, particularly among the growing middle class.

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With plenty of violence, superstition and scandal — all themes Chinese government censors frown upon — these shows probably would never have made it to Chinese television. But through the Internet they have gained millions of fans on video websites that legally license the shows.

Now, the government has indicated in private talks with Internet companies that it plans to close this gap with new rules this year, company employees say.

The regulating agency “truly is currently actively studying a set of plans to specifically manage imported shows on the Internet,” said Spenser Wang, director of government cooperation at the streaming site iQiyi.

China’s streaming-video industry has grown exponentially in recent years, as more people have eschewed the approved television menu of family-friendly soap operas, revolutionary dramas and costume shows. The Shanghai-based Internet research firm iResearch estimated that China’s online video revenue increased 41.9 percent in 2013, reaching 12.81 billion renminbi, or $2 billion.

The online video companies are exploiting policy loopholes to broadcast more foreign programming than is allowed on film and television. Officially, the government limits foreign films to 34 a year and imposes quotas on the number of foreign shows on TV.

Yet websites like iQiyi, Youku Tudou and Sohu provide China’s 600 million Internet users with largely free access to nearly all the latest foreign television shows, as well as hundreds of films and documentaries. Chinese viewers can often watch shows the same day they are broadcast in the United States.

The websites feature legal content licensed from American networks like NBC and CBS.

Domestic dramas and variety shows are still significantly more popular than foreign programming. But American dramas have grown in popularity, particularly among younger, urban audiences.