China reacted furiously on Wednesday to the denial of the Nanjing massacre by a senior manager at Japan's national broadcaster, calling his remarks "a barefaced challenge to international justice".

Naoki Hyakuta dismissed as "propaganda" the accounts of the 1937-8 orgy of murder and rape by Japanese troops as they rampaged through China, in comments made during a stump speech for a right-wing candidate in Sunday's election for Tokyo governor.

In a stinging response Wednesday, Foreign Ministry spokesman Hong Lei urged Japan to "face up" to its history.

Hyakuta's comments were "a barefaced challenge to international justice and human conscience," he said, according to state news agency Xinhua.

"The Nanjing massacre is a brutal crime committed by the Japanese militarism during their invasion of China, which has irrefutable evidence. The international community already had a verdict about it," Hong added.

Right-wing novelist Hyakuta is one of a 12-strong management committee at the publicly-funded Japanese broadcaster.

His comments came after the newly-appointed head of NHK sparked anger with comments on Japan's wartime system of sex slavery and said the station's output should reflect government policy.

Both sets of remarks are likely to fuel fears among some commentators that NHK, one of the world's biggest broadcasters, is falling meekly into line with Prime Minister Shinzo Abe's aggressively nationalist agenda.

"Countries in the world ignored the propaganda produced (by then-Chinese leader Chiang Kai-shek)... that Japan's troops carried out a massacre in Nanjing. Why? There was no such thing," Hyakuta said during a speech on Sunday, according to the Asahi Shimbun.

"During the war there probably were atrocities committed by some members of the military, but that is not limited to the Japanese. There is no reason to teach these things to children in compulsory education," he said.

The "Rape of Nanking" is an exceptionally sensitive issue in Japan's often-fraught relations with China, which says Tokyo has failed to atone for one of the most brutal episodes of its occupation.

China says 300,000 civilians and soldiers died in a spree of killing, rape and destruction in the six weeks after the Japanese military entered the then-capital on December 13, 1937.

Some foreign academics put the number of deaths lower, including China historian Jonathan Spence who estimates that 42,000 soldiers and citizens were killed and 20,000 women raped, many of whom later died.

No respected mainstream historians dispute the massacre.

Japan's government said Tuesday that Hyakuta had done nothing wrong.

Chief Cabinet Secretary Yoshihide Suga told reporters that Hyakuta was entitled to his opinions.

"I'm aware of the reports, but I've learnt (expressing personal views) doesn't violate the Broadcast Law. The government declines to comment on the issue," he told reporters.