(Reuters) - Chinese planemaker COMAC has painted one of its ARJ21 regional jets with C909 branding, aligning with the manufacturer's naming conventions for its other models, according to photos posted on aviation enthusiast forums and Chinese social media.

Although largely symbolic, a possible rebranding ahead of China's main air show in Zhuhai next month signals Beijing's growing intention to present itself as a full-scale alternative to Western plane giants Airbus and Boeing ( BA ).

An ARJ21 plane was photographed with "C909" painted on its blue tail at Shanghai Pudong airport on Sunday by two users of plane-spotting website jetphotos.com and one user of planespotters.net, and other images of it appeared on Chinese social media site Weibo on Monday.

Reuters has been unable to independently verify the photos. COMAC did not immediately respond to a request for comment.

The ARJ21 entered service in 2016 and is operated by various Chinese airlines and Indonesian carrier TransNusa. But market analysts say the regional aircraft, China's first jet to reach commercial production, remains uncompetitive globally.

COMAC's subsequent plane, the single-aisle C919, entered service in 2023 and the planemaker has said it is designing a twin-aisle plane called the C929. The company has also hinted at an even larger C939 in the future.

The C929 was renamed in 2023 from the CR929 after Russia left a China-Russia joint venture developing it.

The photographed plane, painted with registration number B-099A and manufacturing serial number 10156, belongs to COMAC and is registered as an ARJ21 test flight aircraft, according to Flightradar24 tracking data.

On Monday it conducted what appeared to be a test flight from Shanghai Pudong airport, Flightradar24 shows.

The International Civil Aviation Organization's aircraft type designator database still records COMAC's regional jet as the ARJ21. ICAO did not immediately respond to a request for comment.

The practice of renaming models to create a single brand is common in aviation. Airbus in 2018 renamed Bombardier's CSeries the A220 after buying the programme.

COMAC this year has increased sales and production plans and has been marketing its planes outside China. But industry sources caution COMAC is a long way from making inroads internationally, especially without benchmark certifications from the EU - which COMAC is pursuing for the C919 - or the U.S.