Zhang Yimou's latest work The Flowers of War, a movie set against the backdrop of the Nanjing Massacre during the War of Resistance Against Japanese Aggression (1937-45) has re-triggered the debate on movie ratings in China.

The film was rated "R" by the Classification and Rating Administration of the Motion Picture Association of America (MPAA) for its Oscar-qualifying run in Los Angeles, New York and San Francisco in late December, which meant viewers under 17 had to be accompanied by a parent or adult guardian.

Zhang doesn't have to worry about the film's rating back home, as there is no rating system in this country. Children in China can quite easily view adult material that other countries feel might be disturbing to young viewers.

But cultural critics are increasingly worried about the effect scenes involving nudity, profanity or violence might be having on minds of young viewers.

The State Administration of Radio, Film and Television recently published a draft law for the film industry in order to solicit public opinions. While it does contain provisions restricting content such as obscenity, drug abuse, gambling, violence and terror in movies, and one provision bans content that "violates the rights of minors and poisons their mental and spiritual health", it fails to go further by rating movies according to their subject matter and content, and it fails to establish an independent, non-government committee to pre-screen and review movies.

That is to say, the moral judgments on movies will remain firmly in official hands.

We may be surprised to learn that the ratings assigned by the MPAA are not laws. The overwhelming majority of producers submit their movies for ratings. Also, most theaters follow the Classification and Rating Administration's guidelines and enforce its provisions.

The purpose of the MPAA rating system is to help parents decide whether or not to take a child to see a particular movie and the MPAA board of 8-13 adults with parenting experience is supposed to represent mainstream American values.

China also needs a movie rating system to protect its children. Such a system would also make it easier for Chinese filmmakers to decide how far they can go when shooting scenes for specific target audience groups

At present the only restriction on films regarded as "unsuitable for child audiences" is the Circular Concerning the Examination and Rating System for Certain Films introduced in 1989 by the then Ministry of Radio, Film, and Television.

The regulation was first applied to a controversial 1989 film entitled Guafu Cun (The Village of Widows), which had some love scenes and nudity.

But this rating system didn't work very well in protecting child audiences and did not apply to foreign films.

Many films rated "PG" for "Parental Guidance" in the United States, because of their scenes depicting extreme violence, graphic love scenes and horrific subject matter, such as Saving Private Ryan, Bridges of Madison County, Spiderman and The Bone Collector were viewed indiscriminately by children of all ages in this country.

Chinese movies earned a record 10 billion yuan ($1.6 billion) in ticket sales in 2011. Yet without a fair and transparent movie ratings system, box office success may translate to children viewing more scenes of sex and violence.

China needs a movie-rating system that includes enough details to be useful and informative and is simple enough to function.

The author is a senior writer with China Daily.