Tougher regulations on television series produced in the United States may be coming after four shows, including popular comedy The Big Bang Theory, were removed from major online video sites in line with a government order, analysts warned on Monday.

Chinese video websites should learn how to cope with regulatory changes, although this specific development may have a "very limited impact" on profits, they added.

"The industry is poised to see a longer list of banned TV series because the government's grip on the category is obviously tightening," said Su Jie, who specializes in the online video market for Analysys International.

Over the weekend, the State Administration of Press, Publication, Radio, Film and Television told the country's major video sites, including Youku and Sohu, to pull the shows. The agency didn't provide a specific explanation.

All the nation's top video sites declined to comment publicly, but frustration and confusion were evident among those who spoke anonymously.

"We have no clue why the government gave the order and we have nothing to do as of now but follow orders from the authorities," said an employee at Sohu.com Inc's online video branch who declined to be identified.

"A long-term decrease in profits isn't likely, although the forced removal of popular shows will definitely lead to viewer losses," said the employee.

Higher revenues from online videos boosted Sohu's first-quarter advertising revenue by 38 percent year-on-year to $111 million, the company's financial report showed.

"Generally speaking, viewers of US shows have higher education levels and disposable incomes than those who watch domestic and South Korean dramas," according to Su. "US series viewers are the most valuable resource for Youku and Sohu when attracting high-end advertisers."

Xu Hao, an analyst at iResearch Consulting Group, said that cutting popular US shows will mean a loss of viewers and lower advertising earnings. He added that in the future, overseas shows may undergo a harsher review process before being made available online.

For sites that were releasing genuine US shows in China simultaneously with their showings in the US, a review-before-release system means they'll lose page views to platforms distributing pirated copies, said Su from Analysys International.

Huang Xuan, 25, a fan of The Good Wife, one of the shows that's been removed, said she will download the show from an illegal site.