The cavernous building that will house the final assembly line of China's own passenger plane is virtually empty, except for an enormous Chinese flag and slogans to rally the workers who will one day produce the C919.

It is a huge engineering challenge but, if the project proceeds on schedule, a prototype of the single-aisle plane will take to the skies by the end of next year.

Its mission is to compete with US aircraft maker Boeing's 737 and the A320 of European consortium Airbus.

The vast 300-metre (330-yard) long hangar where it will be put together, next to Shanghai's Pudong airport, can hold six planes at a time.

But, despite the ambitious goal, the first major parts have yet to arrive, AFP journalists saw on an exclusive tour of the new production facility -- the first for foreign media.

The plane's builders, the Commercial Aircraft Corp. of China (COMAC), said they recognise the issues, but they have the full financial and political backing of the Communist state and believe they will ultimately be successful.

"We will try (for the first flight) at the end of next year," said Zhang Zhengguo, of COMAC's publicity team.

Total spending on the project is unknown.

Chinese airlines will need nearly 6,000 new planes valued at $780 billion over the next 20 years, according to Boeing, and the government wants some of the huge market to go to its own passenger plane.

China has dreamed of building its own civil aircraft since the 1970s when Jiang Qing, leader Mao Zedong's wife and a member of the notorious "Gang of Four", personally backed an attempt to do so. But the Y-10's heavy weight made it impractical and only three were ever built.

Now China is the world's second largest economy. It has built an auto industry by leveraging joint ventures with foreign companies for technology, developed the world's largest high-speed rail network, and sent humans into orbit.

A patriotic song specially commissioned for COMAC compares the C919 to a "Great Wall in the sky".

- 'We may fall down' -

The roar of jet engines from Boeing and Airbus planes flying over the sprawling factory serve as a reminder of the technological complexities involved.

"We are like a child, Boeing and Airbus are adults," said another COMAC official, who declined to be named. "We may fall down, or walk unsteadily."

Although China claims the C919 is self-developed and manufactured, foreign companies are playing key roles in the project by supplying systems as well as newly developed engines made by French-American venture CFM International.

The narrow body plane, with a range of up to 5,555 kilometres (3,444 miles), can seat a maximum of 174 passengers, according to COMAC.

The first major C919 part to be completed, a single forward fuselage piece, came off the assembly line at a factory in the central province of Jiangxi in May, state media reported.

At a separate sub-assembly line in Shanghai, there are signs of life as workers put together the Spanish machinery which will make the central wing box -- which secures the wing in the body -- and the horizontal part of the tail.

Banners on the wall speak of "storming the gate" and "eating bitterness", echoing political slogans from China's past.

- Iron bird -

At a development centre for the project, the C919 exists only as a model of the cockpit and the "iron bird", a flightless testing platform for control, landing gear and other systems.

The project received a boost in May when Chinese President Xi Jinping visited the company and sat in the model's pilot seat.

"We must, and will, make our own large jetliner," he said, according to state-run media.

COMAC already claims 400 orders for the C919, most from domestic leasing companies and only one from a foreign customer, GE Capital Aviation Services -- a subsidiary of General Electric, the US firm that co-owns engine provider CFM.

A smaller regional jet also under development, the ARJ21, has 253 orders but first deliveries have been delayed by years.

Airlines remain reluctant to order the C919 while it has not been certified by the US Federal Aviation Administration, a crucial step which would enable it to fly in US skies and assure passengers about its safety.

But Marwan Lahoud, director of strategy for Airbus, warned: "The Chinese threat should not be taken lightly."

"The Chinese will make good aircraft and will sell them," he told France's Tribune newspaper this week. "We will not be able to compete with the financial packages they will be able to offer airlines. Only our technological lead will preserve our advantage."