Apple is to face "strengthened supervision" from China's consumer watchdogs, state media reported Friday, as the US computer giant is hit by a barrage of negative publicity and court cases in the country.

China is Apple's second-biggest market, and its iPhones and other products -- many of them made in the country -- are highly popular, although it faces fierce competition from South Korea's Samsung.

State media have carried a series of attacks against Apple, with the People's Daily, the Communist Party's official mouthpiece, running critical items for five consecutive days over alleged double standards in customer service and returns policies.

Apple has denied those accusations in statements to Chinese media but the condemnations have continued unabated, with the newspaper urging consumers to "strike away Apple's unparalleled arrogance" in one of its commentaries.

The State Administration for Industry and Commerce (SAIC) has asked trading standards bodies across the country to step up "contract supervision" on electronics manufacturers "such as Apple", the People's Daily said Friday.

"Local governments are required to... investigate and punish illegal activities in accordance with the law," it quoted the SAIC as saying in an official note.

An SAIC spokesman who declined to be named confirmed the existence of the document to AFP but declined to disclose details.

The People's Daily articles follow reports on state broadcaster CCTV, but users of China's Twitter-like weibos have been split, with some backing Apple and saying state-owned Chinese firms deserved more criticism for poor service.

Speculation has mounted that it is an organised campaign, and columnist and microblogger Lian Peng said he bought a new iPad Friday "on purpose" and will "seriously consider buying an iPhone 5".

"I don't fancy electronic items. But I feel embarrassed if I don't purchase after seeing the bombardment of advertising jointly staged by CCTV and the People's Daily," he wrote.

Kai-Fu Lee compared current events to 2009, when he was the head of Google China and the US search engine firm suffered state media potshots followed by official penalties.

Google effectively shut down its Chinese search engine in 2010 after months of tensions with the government over censorship, and now sends mainland users to its uncensored site in Hong Kong.

But any underlying motive behind the attacks against Apple remains unclear.

China and the US are embroiled in a series of rows over technology and cybersecurity.

A new US spending bill blocks government buying of information technology equipment "produced, manufactured or assembled" by firms "owned, directed or subsidised" by China.

A US research firm said last month a Chinese army unit had stolen "hundreds of terabytes" of data, from mostly US companies.

China dismissed the report as "groundless" and said its defence ministry websites were often subject to hacking attacks originating in the US.

No-one from Apple's China office was available for comment Friday.

The California-based company has also been embroiled in legal disputes in China over alleged intellectual property rights infringements.

Apple appeared in a Shanghai court on Wednesday accused by a Chinese firm of infringing its voice recognition software patent with the iPhone's "Siri" personal assistant.

The state-owned Shanghai Animation Film Studio has also sued Apple in a Beijing court for allegedly selling its movies without approval, seeking compensation of 3.3 million yuan ($530,000), a lawyer representing the studio told AFP on Friday.

Apple last year paid $60 million to Chinese computer maker Shenzhen Proview Technology to settle a dispute over the "iPad" trademark.