.png "English"){kind=small}
Photographs published online and Chinese military sources cited by the Japanese media indicate a test model of the J-20 fighter has been finished, with taxi tests carried out last week at an airfield in southwestern China.
The news comes just days before a visit to Beijing by US Defence Secretary Robert Gates, who will seek to mend military ties cut off a year ago by China when Washington sold billions of dollars in arms to its rival Taiwan.
Experts say the J-20 will eventually rival the US Air Force's F-22, the world's only fully operational next-generation stealth fighter jet -- but not any time soon.
The J-20 "will become fully competitive with the F-22, in capability and perhaps in numbers, around the end of this decade," Rick Fisher, an expert on the Chinese military at the International Assessment and Strategy Centre, a US think tank, told AFP.
Dennis Blasko, an expert on the People's Liberation Army -- the world's largest military force -- said the timeline for development of the jet was "probably considerably longer than what most outside observers would estimate".
China plans to begin test flights of the J-20 as soon as this month, with plans to deploy the jet as early as 2017, Japan's Asahi Shimbun newspaper said, quoting Chinese military sources.
The fighter will be equipped with large missiles and could reach the island of Guam, a US territory in the western Pacific, with aerial refuelling, although it would take 10 to 15 more years to develop technology on a par with that of the US F-22, it said.
In late 2009, the deputy head of China's air force, General He Weirong, said the country's stealth fighter would be operational sometime between 2017 and 2019, reports said.
Officials at China's defence ministry declined immediate comment when contacted by AFP about the reports.
Western military experts expressed doubts over how far the PLA had progressed with the J-20 programme.
"I have yet to see proof of a test flight. And testing for a prototype can take quite some time before production begins," Blasko said.
Other than the United States and China, only a handful of countries are working on so-called next-generation stealth fighters.
In January 2010, Russia unveiled a new aircraft touted as a rival to the US jet, developed by Sukhoi.
According to Fisher, Japan has a homegrown programme, while India is cooperating with Russia.
The news about the J-20 comes at a key moment in Sino-US relations, with Gates due in Beijing on Sunday and Chinese President Hu Jintao to visit Washington later this month.
US military officials and strategists see Beijing as a potential threat to Washington's once unrivalled dominance of the Pacific. Ahead of the visit by Gates, contacts had only resumed at a technical level.
Fisher indeed predicted that the J-20 could become a "serious threat to US air superiority in Asia before the end of the decade".
China's massive annual military spending also has aroused concern among its neighbours. Japan last month labelled Beijing's military build-up a global "concern", citing its increased assertiveness in the East and South China Seas.
China has repeatedly insisted its military growth does not pose any threat.
Defence Minister Liang Guanglie said last week that China was currently beefing up its navy, air force and strategic missile forces, while decreasing its ground forces.
According to defence industry publication Aviation Week, the J-20 is larger than observers expected -- suggesting a long-range capacity and the ability to carry heavy weapons loads.