File photo shows the Y-20, China's homegrown large transport aircraft. Y-20 officially joined the People's Liberation Army Air Force on Wednesday. (Xinhua/Cao Yinan)

Painted grey and carrying national flags and yellow serial numbers on their tails, two Y-20 planes, China's largest homegrown transport aircraft, officially joined the People's Liberation Army (PLA) Air Force on Wednesday.

Designed and manufactured by state-owned aviation giant the Aviation Industry Corporation of China (AVIC), the Y-20 boasts a maximum takeoff weight of around 200 tonnes.

It is ideal for transporting cargo and people over long distances in diverse weather conditions, according to AVIC.

"The Y-20 entering into service marks a crucial step for the Air Force improving its strategic power projection capability," said PLA Air Force spokesperson Shen Jinke.

The Air Force needs more and better transport to better fulfill its military responsibilities, including safeguarding national security as well as domestic and international rescue and relief work, Shen added.

"For China, The Y-20 is key to the building of a strategic air force," said Fang Bing, a professor with the National Defense University PLA China.

Addressing a ceremony trumpeting the planes on Wednesday, Central Military Commission Vice Chairman Xu Qiliang congratulated those who contributed to the research and production of the aircraft.

Xu also called for better aviation design and manufacturing, and equipment maintenance.

Officially codenamed "Kunpeng," after a Chinese mythical bird that can fly for thousands of kilometers, the Y-20 has got the nickname "Chubby Girl" for its a deep and wide fuselage.

The fuselage is designed hold more cargo and larger equipment, which also enables the Y-20 to be developed into other variants in the future, according to AVIC.

Its high reliability, long design life and complex systems all hold competitive edges, said Tang Changhong, chief designer of the aircraft.

China began the Y-20 project in 2007. Only three other countries have the capacity to develop and manufacture such large transport aircraft, "but none would share the know-how," said Tang.

"We could not even get a design drawing for reference. We had to start from scratch, everything from the very beginning."

Nearly 1,000 research and manufacturing facilities helped build the aircraft, and, after years of hard work, their endeavors have paid off.

Y-20 made its maiden flight in January 2013, and debuted at the 10th China International Aviation and Aerospace Exhibition in November 2014.

Last month, the first two Y-20 planes were delivered to the Air Force, after five years of design and manufacture as well as another four years of test flights.

The time between the start of the design and the Y-20's flight was around half that of similar aircraft in other countries.

"China has joined the few nations capable of indigenously developing 200-tonne-level large transport aircraft," said Geng Ruguang, vice general manager of AVIC and the general director of the Y-20 project.

According to AVIC, the Y-20 will be tasked with servicing national defense modernization, disaster relief and carrying international humanitarian aid.

The Y-20 will form a powerful arm of the Air Force and help to boost China's image as a responsible power, Wang Mingliang, professor with Air Force Command College, said.

The Air Force has carried out many airdrop and evacuation tasks responding to earthquakes, floods, fires and storms in China.

It has also provided aid and delivered relief supplies to Pakistan, Mongolia, Thailand, Nepal and other countries as they were hit by disasters in recent years.

"To enhance national strength, China must build up its ability of indigenously designing and producing large aircraft and strengthen its air transport," said Tang Changhong.

In 2006, developing large aircraft was listed as a national key sci-tech project. A decade on, China is eying accelerated development of large aircraft, with the task having been written into the 13th Five-Year Plan, the country's blueprint for the next five years, in March.

"The delivery of the Y-20 marks the realization of a Chinese aviation dream going back decades, and a major breakthrough in sci-tech innovation and high-end equipment manufacturing in China," said Geng Ruguang.