Taiwanese companies should assume their social responsibilities and play a "positive role" in promoting the peaceful development of relations across the Taiwan Strait, China's government said on Wednesday, amid a probe into major Apple supplier Foxconn.

China's tax and land use investigations into Foxconn's operations there have been seized on by the frontrunner to be Taiwan's next president, Lai Ching-te, as an example of Chinese election interference and placing undue pressure on Taiwanese corporates who have invested billions into China.

The Chinese government has not officially confirmed the investigations, first reported by nationalistic, state-backed tabloid the Global Times on Sunday. China claims Taiwan as its own territory.

Asked about the investigation at a routine news conference in Beijing, Zhu Fenglian, a spokesperson for China's Taiwan Affairs Office, did not confirm the probe or refer to Foxconn.

"Relevant mainland departments treat all enterprises equally in accordance with the law and regulations, and it is a normal law enforcement act to carry out law-abiding investigations," she said.

China's policy of respecting, caring for and benefiting people from Taiwan will not change, and the government will as always support Taiwanese businessmen and companies to invest and create a good environment for their development, Zhu said.

She signalled China expected these companies to play a political role.

"While sharing development benefits and growth dividends on the mainland and achieving rapid development, Taiwan enterprises should also assume corresponding social responsibilities and play a positive role in promoting the peaceful development of cross-Straits relations."

Zhu did not elaborate.

On Tuesday, Taiwan Vice President Lai, the ruling Democratic Progressive Party's (DPP) candidate for president at January elections, hit out at China over its probe of Foxconn, saying Beijing should "cherish" Taiwanese companies and not put pressure on them during an election.

China believes Lai, who is leading opinion polls, is a separatist bent on a formal declaration of independence. Lai says he will maintain the status quo with China, and has repeatedly offered talks which Beijing has rebuffed.

Zhu, in a step up of China's attacks against Lai, said he was "duping people" by both trying to "use weapons to seek independence" and also calling for dialogue.

"As pointed out by the media on the island, Lai Ching-te has now changing from a Taiwan independence maniac to a Taiwan independence liar," she said.

"This comment has hit the nail on the head and is appropriate. I believe that the majority of Taiwanese compatriots have a clear understanding of this."

Foxconn shares closed up 0.7% on Wednesday, rebounding after two straight days of falls. The broader Taipei index ended 0.3% higher.