The proposal has dismayed filmmakers and inspired moviegoers to vent on social media on Tuesday.

"Officials of the national movie bureau are making rules (from out of thin air)," film fan Trung Pham declared on Facebook.

Prominent directors Nguyen Thanh and Van Bui Tuan Dung aired complaints in Vietnamese media, suggesting that the length of sex scenes matters much less than the artistry.

"Some shots are under a second," Van told the Thanh Nien newspaper, "but they are unbearable anyway."

Ngo Phuong Lan, chief of the national movie bureau, disclosed the proposal at a meeting Friday. Sex scenes would be limited to five seconds in length, with a limit of three such scenes per film.

A new ratings system would also restrict certain films to viewers at least 18 years of age. Mr Lan said the public's comments would be considered before the rules are finalised.

Defining a sex scene is problematic. While pornography is illegal in Vietnam, a scene featuring "a totally nude actress" would be subject to the limits.

But confusion persists over the censors' regard for male nudity, raising complaints of sexism, Thanh Nien reported.

Nguyen Van Nhiem, head of Studio A Vietnam, said sex is natural and artists should not face time limits on their craft, but rather have freedom to express passion artfully.

Facebook user Oc Lac expressed puzzlement over the censors' priorities.

"What they should do," Oc Lac said, "is ban porn scenes that are rampant on the internet."

Deutsche Presse Agentur - September 23, 2015