China's rapidly modernizing air force is planning a display of its new military might for its 60th anniversary, showcasing a wide-ranging technical upgrade that has boosted its capabilities, though it still lags far behind its main rival, the United States.

The People's Liberation Army Air Force is marking the occasion this Sunday with an aerial show and skydiving exhibition, using some of the state-of-the-art combat aircraft that have replaced hundreds of antiquated MIG fighters.

While only about 20 percent of those planes are on a level with those deployed by the West, that ratio is already double what it was five years ago, said Cheung Tai Ming, an expert on the Chinese military at the University of California, San Diego.

In another two decades, it could become the region's dominant air force, Cheung said.

"In terms of hardware," he said, China's air force "is making strides but still has long way to go."

China's air force and navy have been prime beneficiaries of huge defense spending increases as the primarily land-based, defensively oriented military boosts its ability to project force far from the nation's borders.

Tanker planes, AWACS and other support aircraft have been added to extend the reach and effectiveness of the air force's advanced Russian Sukhoi and domestically developed J-10 fighters.

The force has more than 600,000 members and about 2,000 aircraft — making it the largest in Asia — but still far smaller than the United States Air Force fleet, which has more than 5,500 aircraft and nearly 327,500 active service personnel.

The improvements are primarily seen as augmenting the force's key mission of protecting China's borders and preventing formal independence for Taiwan, the self-governing island that Beijing claims as its own territory.

China's air force is largely considered superior to Taiwan's in both quantity and quality, while the 1,300 short and medium range missiles deployed opposite the island could deal severe blows to Taiwanese airfields and anti-aircraft defenses.

Yet planning for any conflict over Taiwan would have to factor in the possibility of intervention by the U.S., which is bound by law to help ensure the island's defense. Under those circumstances, China's air force would very likely be outmatched and outgunned.

The force's key problems include a lack of actual combat experience and outdated training and tactics. Its last combat experience was in the brief 1979 war with Vietnam, in which it played a mainly symbolic role. Other woes include a lack of integration with naval and ground forces, limited surveillance and reconnoissance capabilities, and problems recruiting and retaining pilots.

In addition, China's air force doesn't have enough planes to mount a major airlift of equipment and supplies in either a combat or humanitarian relief operation. Troops taking part in a recent nationwide training exercise flew by commercial jet, and the lack of capacity has frustrated China's aspirations to play a greater regional role in humanitarian relief operations.

While the air force mobilized massively to deal with last year's Sichuan earthquake, bad weather forced the cancellation of several attempts to fly in men and equipment. A much ballyhooed mission to parachute in troops bordered on farce, requiring the better part of two days and resulting in the dropping of a mere 15 soldiers.

Flight safety is another issue. A series of disasters in recent years have led to the firing of some top officers, but intense secrecy surrounding all mishaps makes it difficult to assess the PLAAF's record. Guards seized footage of one recent accident shot by state television, according to the cameraman, who spoke on condition of anonymity for fear of official retribution.

Sunday's celebration is to include aerial displays by both the force's standby J-7 fighters and the newer J-10, along with men's and women's teams skydiving from helicopters.

The event is the third major military display this year following an international naval review and a national day military parade featuring hundreds of tanks and other armored vehicles.

Beijing insists the events are intended only to boost public pride and confidence in the armed force, although they have also renewed concern abroad about the ultimate aims of China's military expansion.

Such displays "underscore the rise in the country's comprehensive national power and the firm material and technological foundation provided for air force modernization," the force's commander Xu Qiliang told the PLA Daily newspaper in an interview published this week.