China's Navy has launched a new electronic reconnaissance ship, state media said on Thursday, the latest addition to an expanding fleet and as Beijing's new assertiveness to territorial claims in the South China Sea fuels tensions.

The People's Liberation Army (PLA) now operates six electronic reconnaissance vessels, the official English-language China Daily newspaper said, noting that the PLA "has never made public so many details about its intelligence collection ships".

Last year, the PLA Navy commissioned 18 ships, including missile destroyers, corvettes and guided missile frigates, the paper said.

China has also said it is building a second aircraft carrier. China's only carrier is the second-hand, Soviet-built Liaoning, which this week unsettled neighbours with drills in the disputed South China Sea.

The new electronic reconnaissance ship, the CNS Kaiyangxing or Mizar, with hull code 856, was on Tuesday delivered to a combat support flotilla of the North Sea Fleet at the eastern port of Qingdao, the China Daily said.

"The Kaiyangxing is capable of conducting all-weather, round-the-clock reconnaissance on multiple and different targets," the newspaper said, citing Chinese defence media as comparing it to sophisticated vessels only produced by countries with advanced militaries, such as the United States and Russia.

Regional naval officials say Chinese ships now increasingly track and shadow US and Japanese warships in the South China and East China seas, even during routine deployments.

China claims almost of the South China Sea, believed to have huge deposits of oil and gas, through which about $5 trillion in ship-borne trade passes every year, and has been building up military facilities like runways on the islands it controls.

Brunei, Malaysia, the Philippines, Taiwan and Vietnam also have claims.

China says it has no hostile intent and wants to manage the dispute through bilateral talks with the other claimants. But Beijing has been involved in a diplomatic spat with Washington over ship and aircraft patrols in the region.

On Wednesday, US President-elect Donald Trump's nominee for secretary of state, Rex Tillerson, said China should be denied access to islands it has built and placed military assets on in the South China Sea.