EMMA ALBERICI, PRESENTER: One of the world's biggest and most influential public broadcasters, NHK in Japan, is under attack. The conservative Abe Government in Japan has made a series of right-wing appointments to NHK's board. They're threatening the broadcaster's credibility and neutrality by instructing journalists on how to report. The NHK chairman has had to apologise over comments he made inferring the station was doing the Government's bidding. North Asia correspondent Matthew Carney reports from Tokyo.

MATTHEW CARNEY, REPORTER: Japanese Prime Minister Shinzo Abe says he wants to make his country great again. He's in the process of reforming Japan's pacifist constitution. At the same time, he's playing down Japan's war-time past while increasing Defence budgets. It's a nationalist agenda, but he wants the public broadcaster, NHK, to sell his vision.

YASUSHI KAWASAKI, FORMER NHK POLITICAL REPORTER (voiceover translation): NHK has great influence as a public broadcaster. It's easier for Abe to do politics if NHK supports him, so he has started to interfere in NHK in various ways.

MATTHEW CARNEY: Prime Minister Abe has engineered changes at the top by appointing four controversial new board members. Professor Michiko Hasegawa is a right-wing academic who believes women's primary role is to give birth and raise children, not to work. In her latest essay, she writes, "Such divisions of roles based on sex is very natural for humans as mammals." Another new board member, nationalist writer Naoki Hyakuta, says the Nanjing Massacre of 1937 in China by Japanese forces never happened. Historians say up to 300,000 were killed.

But the new chairperson of NHK, Katsuhito Momii, who has the ultimate editorial control, is causing the biggest worry. He told NHK journalists at a press conference, "It would not do for us to say left when the Government is saying right."

Professor Kawasaki was a senior journalist at NHK for 35 years.

YASUSHI KAWASAKI (voiceover translation): I'm disgusted by this. There's some kind of right-wing revolution happening in Japan and they want NHK to be part of it. It threatens the existence of NHK as a public broadcaster and it will become the same as the broadcaster in North Korea.

MATTHEW CARNEY: Former NHK reporter and presenter Jun Hori feels there is increasing pressure within the public broadcaster to tow the Government's line.

JUN HORI, FORMER NHK REPORTER (voiceover translation): I quit, but my colleagues who make programs at NHK say it's very difficult to get a green light on story proposals. Some subject matters are very sensitive for the Government, such as the contaminated water problem at the Fukushima nuclear plant.

MATTHEW CARNEY: Hori left the organisation after he was told he could not be critical of the Government's response to the Fukushima nuclear disaster.

Another senior presenter has recently joined him after he was instructed not to report on Prime Minister Abe's plan to use nuclear power again.

JUN HORI (voiceover translation): When I tried to report about my news coverage, they would say, "Let's not report about that." So it's self-censorship. They don't tell you, "You can't do this," but they think if we report this, it might cause a big problem. We might get a lot of complaints if we report this.

MATTHEW CARNEY: Japan's broadcasting act guarantees NHK's editorial independence, but the public has started to question the organisation's credibility. Thousands of viewers have started to call in to complain about the Prime Minister's appointments.

Lateline approached the NHK chairman, Mr Momii, and board members as well as the Government for a response. They all declined. But Mr Momii was hauled before the Japanese Parliament and grilled by the Opposition.

KAZUHIRO HARAGUCHI, OPPOSITION MP (voiceover translation): Please answer clearly. Were your comments legitimate or not according to the broadcasting act? If you can't answer this, I think you should resign.

KATSUHITO MOMII, NHK CHAIRMAN (voiceover translation): I made comments before I could properly organise my personal views and my opinions as a chairman. I feel sorry for causing trouble to the viewers and to other people. I intend to put all my heart and soul into making NHK a broadcaster that can be trusted.

MATTHEW CARNEY: But many feel the damage has already been done. The chairperson only retracted his comments after prolonged political pressure and public outrage.

Matthew Carney, Lateline.