It's not at all uncommon for people to get a little bit hyperbolic and compare things or people they don't like to the Nazis. There are "soup Nazis" and "grammar Nazis." The attack is so common there's even a special law to handle it: Godwin's Law of Nazi Analogies. According to Godwin's law, anyone who compares another to the Nazis automatically loses the debate—no one was the Nazis but the Nazis.
This makes it all the more striking when Michael Kirby, the chair of the United Nations Human Rights Commission's investigation into North Korea, compared the country to the Nazis.
North Korea’s leadership is committing systematic and appalling abuses against its own citizens on a scale unparalleled in the modern world, crimes against humanity with strong resemblances to those committed by the Nazis, an inquiry has concluded. [...]
At a press conference to launch the report, Kirby said there were "many parallels" between the evidence he had heard and crimes committed by the Nazis and their allies in the second world war. He noted the evidence of one prison camp inmate who said his duties involved burning the bodies of those who had starved to death and using the remains as fertiliser.
In the report, the U.N. commission detailed, sometimes in explicit detail, how North Korea is engaged in systematic ideological indoctrination, politically motivated starvation, abductions, enslavement, rape, torture, executions, and other crimes against humanity. From the report:
In the political prison camps of the Democratic People’s Republic of Korea, the inmate population has been gradually eliminated through deliberate starvation, forced labour, executions, torture, rape and the denial of reproductive rights enforced through punishment, forced abortion and infanticide. The commission estimates that hundreds of thousands of political prisoners have perished in these camps over the past five decades. The unspeakable atrocities that are being committed against inmates of the kwanliso political prison camps resemble the horrors of camps that totalitarian States established during the twentieth century.
If you're interested in getting a more specific sense of that, the Sydney Morning Herald is carrying a series of drawings done by Kim Kwang-Il, who had spent two years in a North Korean prison. The drawings depict the things Kim saw during his stay in prison.
The U.N. report is also critical of the world's response to the conditions in North Korea. “The fact that the Democratic People’s Republic of Korea, as a State Member of the United Nations, has for decades pursued policies involving crimes that shock the conscience of humanity raises questions about the inadequacy of the response of the international community," the report says.
Holding up a copy of the report, Kirby said other nations could not say of North Korea, as happened with the Nazis, that they did not know the extent of the crimes: "Now the international community does know. There will be no excusing a failure of action because we didn't know. It's too long now. The suffering and the tears of the people of North Korea demand action."
The U.N. report recommends that Kim Jong-un and other leaders of North Korea stand trial at the International Criminal Court in The Hague for crimes against humanity.