(Repeats story from late Thursday with no changes to text)

By Sophie Yu and Stella Qiu

BEIJING/SYDNEY, Sept 29 (Reuters) - China held a ceremony on Thursday to certify its C919 narrowbody passenger jet, photos on social media showed, representing a major milestone in the country's ambitions to challenge Airbus and Boeing in commercial aerospace.

The plane, produced by state-owned manufacturer Commercial Aircraft Corp of China (COMAC), had been widely expected to be certified by the end of the month after two aircraft flew to Beijing on Sept. 13. A sign in one of the photos said "C919 aircraft type certificate issuance ceremony" in Chinese.

COMAC did not respond immediately to a request for comment.

The C919, launched 14 years ago and designed to carry up to 168 passengers, will compete against the popular Airbus A320neo and Boeing 737 MAX families in the world's second-biggest aviation market as China looks to boost its technological self-reliance amid trade tensions.

Although the plane is assembled in China, it relies heavily on Western components, including engines and avionics, from companies including GE, Safran and Honeywell International.

Tough U.S. export licensing rules have led to delays in sourcing parts and remain a key risk to ramped up production until China replaces foreign engines and components with homegrown technology.

Richard Aboulafia, U.S.-based managing director of AeroDynamic Advisory, said the plane seems like a relic of a bygone era of increasing integration between China and the West.

"Thus, we have an aircraft that is only superficially Chinese but is actually powered by Western technologies and systems," he said. "Turning it into a genuine Chinese aircraft would take well over a decade and many billions of dollars."

The type of certificate granted on Thursday means it can be delivered to the first customer, China Eastern Airlines Corp Ltd , though local media have reported the plane is unlikely to enter commercial service with passengers until next year.

The C919 has never made an appearance at the country's premier aviation event, Airshow China and it is unclear whether it will be on display or flown at the show in November.

COMAC will also need a separate production certificate before it can ramp up mass production of the plane, meaning its impact on the global aircraft market could remain limited given Airbus and Boeing produce dozens of narrowbodies a month.

"The C919 will gradually begin to replace single-aisle aircraft made by Boeing and Airbus," in China, a research note by Huaxi Securities said this month. "In the next 20 years, China's demand for narrowbody passenger aircraft like the C919 will be on average 300 per year."