BEIJING, May 14 (Reuters) - China's state-owned aircraft manufacturer COMAC is working on preliminary designs for a new widebody jet called the C939, the South China Morning Post reported, citing a source familiar with the matter.

Commercial Aircraft Corporation of China, which is expanding production facilities for its C919 narrowbody jets, has sketched out preliminary designs for the new aircraft, according to the report published late on Monday.

It would be many years before the early concepts materialise into a testable prototype, according to the report, which also did not provide specific details on the proposed plane.

The new jet would expand commercial operations for COMAC amid ambitions by Beijing to take market share from industry leaders Airbus and Boeing.

The C919 has so far gained more than 1,000 orders, but mostly from Chinese airlines and aircraft lessors including China Eastern Airlines, the first user of the jet.

COMAC's other in-development widebody plane, the C929, is designed to travel international routes of up to 12,000 km (7,500 miles). It is speculated to be on par with some aspects of mainstream competitors like Boeing's 787 Dreamliner, a second source said according to the report, adding that progress was "in full swing".

China has said it wants to secure broader international recognition for the C919 this year. Last year, government-backed media The Paper said China expected to reach annual production capacity of 150 C919s in five years. (Reporting by Bernard Orr; Editing by Jamie Freed)