A bevy of big-screen luminaries including Luc Besson and Arnold Schwarzenegger descended on Beijing recently for a star-studded international film festival, but art-house directors raised the alarm as authorities block a wave of independent cultural events.

Seeking to raise its "soft power" and standing on the world cultural stage, China is pushing its cinema industry with events such as last week's Beijing International Film Festival (BIFF).

State-run media trumpeted the competition's "A-list jury" -- chaired by Besson -- and said the event generated $2.2 billion in new contracts.

But the drive has been accompanied by a harsh crackdown on China's independent filmmakers, whose efforts to create works largely outside the state censorship system have been met with escalating political and financial pressure -- and even violence.

"The hardest thing is deducing where the line is," director and producer Vivian Qu said at a roundtable.

"Over the years, as the Chinese film market grew bigger and bigger, the words 'art-house' and 'independent' and 'underground' have seemed much more sensitive than before."

"I really don't know where the line is right now," she added. "It keeps moving."

The cinema clampdown is part of a broader stifling of civil society since President Xi Jinping took office two years ago, with the Communist Party targeting activists, human rights lawyers and journalists, as it seeks to prevent any challenge to its rule.

In Beijing alone, authorities have recently forced the cancellations of a wide range of independent events, including several music festivals due this weekend, an Earth Day celebration, a benefit for the Beijing LGBT Centre, and a craft beer fair that drew 8,000 people last year.

"Large gatherings are being cancelled left and right," its sponsors Great Leap Brewing noted.

- 'Quite naive' -

Authorities initially turned a blind eye -- or even tacitly supported -- independent cinema events in China, which go back more than a decade.

The China Independent Film Festival, one of the country's premier celebrations of art-house cinema, was first launched at a provincial library in the southwestern city of Kunming in 2003.

Participants were under the impression that it "was almost official", according to organiser Zhang Xianmin, a Beijing Film Academy professor.

"The beginning was quite naive, I would say," he said.

As the event became more professional, it came under increasing pressure. Held more recently in Nanjing, it was shut down in 2012 and reduced in size the following year. The 2014 festival was allowed to proceed, although organisers only minimally publicised the event in order to avoid government attention.

Zhang himself has suffered official harassment, he said, with authorities at times limiting his travel outside China, investigating his finances, and doing "everything you could imagine" to exert pressure on him to halt his activities.

Last year police shut down another prominent cinema forum, the Beijing Independent Film Festival, and detained two of its organisers.

Dozens of unidentified men claiming to be villagers stood guard outside the venue in a Beijing suburb, roughing up journalists and others who approached.

A separate, long-running documentary film festival was cancelled in 2011.

- 'Socialist core values' -

Authorities are ramping up state-backed cultural efforts at the same time as tightening control over the independent film sphere.

Xi last year urged artists to "embody socialist core values in a lively and vivid way" in their works, to "uphold Chinese spirit" and "rally Chinese strength", the official news agency Xinhua reported.

Actress Yang Lina, who has also directed several documentaries, said that "mainstream movies are the only possibility" on the BIFF programme. "I feel very strongly that that cinema has nothing to do with me," she added.

The State Council Information Office, the propaganda arm of China's cabinet, also unveiled a three-year deal in March under which The Discovery Channel will air an hour of Beijing-approved, China-themed programming each week, reaching 90 million viewers in 37 countries and territories.

Diao Yinan's contemporary noir "Black Coal, Thin Ice", which Qu produced, took home the Berlin Film Festival's prestigious Golden Bear last year.

But officials passed over the gritty cop thriller when it came to nominations for the best foreign film Oscar, instead submitting tamer Chinese-French co-production "The Nightingale".

"I wasn't surprised," said Qu. "Of course it's not their ideal film to represent the country."