China's armed forces have been instructed to raise their fighting ability in 2013, state media reported Tuesday, amid heightened tensions with Japan over disputed islands.

In 2013, "the PLA and the Chinese People's Armed Police Force should focus closely on the objective of being able to fight and win a battle," according to a report in the overseas edition of the People's Daily newspaper, the Communist Party organ.

The directive came in a document released at the beginning of the year by the People's Liberation Army (PLA) General Staff on military training in 2013, said the report, republished from a website linked to a PLA newspaper.

To prepare for combat, the armed forces must also "vigorously strengthen real-combat-like military training" and intensify efforts to cultivate high-calibre military personnel, the report said.

The report made no mention of the dispute with Tokyo over islands in the East China Sea, which are controlled by Japan as the Senkakus but also claimed by China as the Diaoyus.

A report in state media early last year on military objectives for 2012 did not call on the military to be ready for combat and was more general, focusing on issues including training reform and promoting information technology.

The maritime dispute, which has simmered off and on for years, intensified last year when the Japanese government nationalised islands in the small chain it did not already own, triggering anger and protests in China.

Both sides have scrambled fighter jets to the area in recent weeks in a further escalation, though no actual clashes have taken place.

Japanese public broadcaster NHK reported Monday that Japan will deploy two more patrol ships to boost its defence of the islands and has conducted its first drill simulating the recapture of an isle seized by enemy forces.

Japan occupied parts of China for several decades in the first half of the 20th century, and the countries have fought two wars, one from 1894-95 and the second from 1937-1945, which was part of the broader Second World War.

China has become increasingly assertive over its territorial claims in disputes with its neighbours as its economic and military power have expanded.

The Asian giant already has the world's largest armed forces and its defence budget has seen double-digit increases every year for much of the last decade, rattling the United States, which is forging ahead with plans to expand its own military power in Asia.

China has made advances in satellite technology and invested in advanced weaponry including its first aircraft carrier but it remains technologically far behind the United States.