The Chengdu J-20 fighter has entered service with the Chinese air force, as reports of emerge of progress with indigenous engines.

A brief, three-line statement from the Chinese ministry of defence said the developmental type had entered service, but added little else.

It is not clear exactly how many have entered service, but Chinese defence chatrooms suggest the number of in-service examples could be six.

There is also speculation that there is progress with the twin-engined type's engines. Early examples were powered by a Russian engine, the Saturn AL-31F, or a Chinese engine, the Shenyang WS-10. Now, media reports suggest the type will receive the more powerful WS-15 engine, which allegedly will allow the J-20 to "super-cruise" – or fly supersonic speeds without afterburner.

The J-20, which first emerged on Chinese defence sites in late 2010, made its public debut at last year's Airshow China in Zhuhai, with two examples overflying the crowd.