BEIJING, Dec. 13 -- China on Saturday observed its first National Memorial Day for Nanjing Massacre Victims, and the commemorative service gained worldwide media attention.

Singapore's South China Morning Post reported that Chinese President Xi Jinping unleashed at a solemn ceremony some of his sharpest words to date against Japan's wartime atrocities in China more than seven decades ago.

Xi and others gathered at a memorial hall in Nanjing, where 77 years ago invading Japanese soldiers slaughtered more than 300,000 people, mostly unresisting civilians, the newspaper said.

The newspaper quoted Xi as calling the massacre "a horrendous crime against humanity and a very dark page in the history of mankind" and stressing that history should not be altered with the passing of time, and facts not erased by crafty denial.

French news agency AFP noted that China for the first time held a national day of remembrance for the Japanese military rampage that killed 300,000 people, and cited Xi as saying that no one can deny the Nanjing Massacre.

The crowd, who attended a ceremony in Nanjing to mark the 77th anniversary of the massacre, sang China's national anthem and observed a moment of silence as a siren symbolizing grief blared and the Chinese national flag flew at half-mast under clear skies, AFP noted.

In an online report, BBC said Xi criticized Japanese nationalists for denying Japan's wartime atrocity in Nanjing.

Xi told survivors that to deny a crime was to repeat it, but he insisted that the ceremony was to promote peace, not prolong hatred, BBC said.

Japan's Kyodo News Agency noted that in preparation for the state commemoration, the city of Nanjing decorated its streets with enormous banners, urging the public to "Inscribe history in your memory" and "Never forget our national humiliation."

Japan's Asahi Shimbun said on its website that in February, China designated Sept. 3 as the Victory Day of the Chinese People's War of Resistance Against Japanese Aggression, and Dec. 13 as the National Memorial Day for Nanjing Massacre Victims, which shows that China attaches great importance to that part of history at a national level.

The Associated Press (AP) reported that Xi and other Chinese leaders attended a ceremony on the 77th anniversary of the Nanking Massacre to preserve memories of Japan's brutal invasion.

Addressing soldiers, students and survivors of the December 1937 killings carried out by occupying Japanese troops, Xi slammed Japanese ultra-nationalists who seek to deny the massacre, AP noted.

Invading Japanese troops captured Nanjing, then China's capital, on Dec. 13, 1937, and started a 40-odd-day slaughter. More than 300,000 Chinese civilians and unarmed soldiers were murdered and about 20,000 women were raped.

"Anyone who tries to deny the massacre will not be allowed by history, the souls of the 300,000 deceased victims, the 1.3 billion Chinese people, and all people who love peace and justice in the world," Xi said.

"Only if everyone cherishes and safeguards peace, and only if everyone remembers the bitter lessons of war, can there be hope for peace," he said.

Meanwhile, Xi said the Chinese and Japanese people should live in friendship from generation to generation and make joint efforts to contribute to the peace of humanity.

"We should not bear hatred against an entire nation just because a small minority of militarists launched aggressive wars. The responsibility for war crimes lies with a few militarists, but not the people. However, we cannot at any time forget the severe crimes committed by aggressors," he said.

People who love peace and justice must remain highly cautious and firmly oppose words and actions that glorify war, he added.