HONG KONG — Hong Kong’s biz was in a buoyant mood at the start of the 35th Hong Kong Film Festival on Sunday, eager to leverage its position as the gateway to China, the world’s biggest developing film market.

While restrictions on the number of foreign movies allowed to play in China make it a difficult market for Hollywood to crack, Hong Kong is keen to offer itself as a route for partnership and collaboration in the Mainland, both in co-production and in exhibition.

China’s quota of around 20 foreign movies on a revenue-sharing basis does not apply in Hong Kong, and the territory has thrived because of its close links to the Mainland Chinese market. Nearly every major Hong Kong filmmaker now has an office in Beijing, and expertise and talent from the territory has been the foundation for an astonishing rise in the biz in China.

Wilfred Wong, chairman of the HKFF Society, acknowledged this closeness at the opening of the fest, which also includes the Filmart film and TV market and the Hong Kong-Asia Film Financing Forum.

“HKFF has contributed and continues to contribute to the development of Hong Kong as the hub of our region’s cinema,” said Wong.

The Chinese box office surged 64% in 2010, flying past the $1.5 billion mark, and two of the year’s biggest hits — “Aftershock” and “Let the Bullets Fly” — were made with a combination of local and international coin.

One of the big discussion points at Filmart will be whether the B.O. can grow even more without the help of an “Avatar”-sized project.

There was a subdued backdrop to the opening gala at the Hong Kong Convention and Exhibition Center and UA Cityplaza because of Japan’s earthquake, tsunami and nuclear disasters, and many industry figures from the regional giant have canceled their appearances at the fest.

“Ever since the Hong Kong Film Festival started 35 years ago, Japanese film has occupied an important place at the event. Our Japanese friends in the film industry have supported the festival continuously,” said Wong.

“At this difficult time, I want to deliver our sincere condolences and best wishes to the entire Japanese people.”

This year’s Filmart has nearly 600 exhibitors from more than 20 countries and regions, and will feature more screenings, preems, seminars, special events and networking opportunities than ever.

The event unspooled two opening films — “Don’t Go Breaking My Heart,” a joint effort by Johnnie To and Wai Ka-fai, and “Quattro Hong Kong 2.”

Latter is an omnibus movie about Hong Kong, jointly helmed by Thailand’s Apichatpong Weerasethakul, who won the Cannes Palme d’Or for “Uncle Boonmee Who Can Recall His Past Lives,” Philippines helmer Brillante Mendoza, who won Cannes’ director laurels for 2009’s “Kinatay,” as well as Ho Yuhang from Malaysia and Hong Kong legend Stanley Kwan.

The fest also marks the 20th anniversary of Fortissimo Films, which is acknowledged as helping to strengthen Hong Kong’s position in the international distribution and sales circuit with its range of Asian films.

Filmart will host the inaugural U.S. Pavilion, organized by the Independent Film & TV Alliance and the Paris-based Assn. Ateliers du Cinema Europeen.

Co-production Lab Hong Kong was also launched at Filmart, providing a platform for producers from Europe and Asia to connect and explore business opportunities via a number of on-site presentations, screenings and case studies on co-production and distribution in European Union and Asian markets.

Filmart will also host TV World, Animation & Digital Entertainment World and Equipment & Post-Production Services Pavilion.

In all, fest will screen 335 pics from 56 countries in venues around the city through April 5, of which 59 are world, international or Asian premieres.