Two pilots in a squadron conducting fighter jet take-off and landing tests for China's lone aircraft carrier were killed during trials, state media reported, offering a rare glimpse into the secretive project.

The revelation of the deaths came in a report last week on the signing of an order of commendation for the crew of China's first carrier-based jet fighter, the J-15.

"Two test pilots of the squadron sacrificed their lives during the tests," the official Xinhua news agency reported on August 27.

No details were given on exactly how or when the pilots were killed or the timing of the tests.

China's sole aircraft carrier, the 300-metre (1,000-foot) Liaoning -- a Soviet-era vessel Beijing bought from Ukraine -- was commissioned in September 2012.

The Xinhua report said that Chinese President Xi Jinping signed the commendation order for the squadron, part of the People's Liberation Army (PLA) Air Force.

The commendation was given to the squadron "for successfully conducting the take-off and landing tests of J-15 fighters" on the carrier.

"The order spoke highly of the squadron in the exploration and development of the J-15 fighter jet," the report said.

The report also said that Dai Mingmeng, identified as the first J-15 pilot to carry out a successful take-off and landing on the Liaoning, received an honorary title as an individual.

Military accidents and equipment malfunctions are rarely reported in China, where news about the armed forces is tightly controlled.

The military's official People's Liberation Army Daily in a report posted on the defence ministry website Wednesday said that China honoured a submarine captain for averting an underwater "emergency" after his crew reportedly saved the vessel from sinking.

Wang Hongli, commander of submarine 372, was praised by the Central Military Commission for "successfully dealing with a major sudden dangerous situation" during an underwater mission.

In April the paper reported that the submarine had been hit by a sudden change in water density while patrolling in an area of the sea "thousands of metres deep".