A senior NHK manager who denied any massacre at Nanjing during the 1930s did nothing wrong, Japan's government said Tuesday, as another storm brewed over the integrity of the national broadcaster.

Naoki Hyakuta, one of a 12-strong management committee responsible for programming policy and budget-setting at the publicly-funded broadcaster, dismissed as "propaganda" the accounts of the 1937-8 orgy of murder and rape by Japanese troops as they rampaged through China.

The comments, made during a stump speech for a right-wing candidate in Sunday's election for Tokyo governor, come 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.

They appear set 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 mainstream respected historians dispute the massacre.

Chief Cabinet Secretary Yoshihide Suga told reporters Tuesday that Hyakuta, a noted right-wing novelist, 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.

Four of the 12 members of the management committee, including Hyakuta, were appointed by conservative Abe late last year.

The Broadcast Law bans committee members taking a senior role in a political party but does not bar them from becoming regular party members or from making political donations.

However, the code of conduct for the committee says its members "need to be aware of their mission of serving... healthy democracy by ensuring fair and politically neutral broadcasting".

Hyakuta's comments followed a controversy caused when new NHK director general Katsuto Momii said the Japanese Imperial Army's system of wartime sex slavery was commonplace.

He subsequently apologised for the statement, blaming his inexperience in press conferences, but refused to retract his assertion that the broadcaster's editorial output should cleave to the government's line.

Those comments, along with the resignation of a noted academic who had been told to avoid criticising nuclear power until after the Tokyo governor's election, have fuelled fears that NHK's editorial independence had been compromised.