Three quarters of a century after Japanese soldiers butchered her family and left her for dead, Xia Shuqin says she relives her terror with every denial that the Nanjing Massacre ever happened.

As the Imperial Japanese Army entered China's then capital city on December 13, 1937, Xia heard pounding at the door.

Within minutes, seven of her family lay dead, killed by invading troops on the first day of two months of slaughter, rape and destruction now known as the Nanjing Massacre.

Part of the conflicts that led up to the Second World War, it stands as the Japanese military's worst atrocity and remains a bitter strain on the two countries' relationship.

Xia's father was shot as he opened the door, before the troops dragged her mother from under a table, still clutching Xia's one-year-old sister.

Both were bayoneted to death -- but not before Xia's mother was gang-raped.

"They threw my sister to the ground and held my mother on the table, ripping at her clothes," she told AFP, her voice breaking.

Two children from the neighbouring house were also killed as Xia hid under the bedclothes in a back room along with her three other sisters, her grandparents sitting on the bed.

For a moment there was silence, then the troops entered, shooting her grandparents in the head before raping and killing her 15- and 13-year-old sisters.

"I was only eight years old at the time, but I knew what had happened to my older sisters, that they had been raped and had died enduring terrible pain and suffering," she said.

"I cried so much that I could barely see anymore. It makes me sad every time I think about it."

Xia was stabbed three times in her back and shoulders and passed out. She woke to find she and her four-year-old sister were the only ones to have survived the slaughter.

The two girls hid among the decaying corpses for 10 days before an elderly couple found them and took them to the International Safety Zone, a makeshift refugee camp set up by foreigners who had stayed in Nanjing to try to prevent further killings.

The massacre continues to have a deep impact on modern-day relations between China and Japan, not least because both sides differ on the scale of carnage.

China says 300,000 people were killed, while in an inconclusive joint study two years ago the Japanese side pointed to "various estimates" ranging from as low as 20,000 to 200,000.

But some fringe analysts and ultraconservative politicians in Japan dispute that atrocities ever took place in the city, known as Nanking at the time.

"I am over 80 years old now and I am still receiving this kind of bullying and humiliation," says Xia, who has spent the last 12 years fighting Japanese deniers through the courts.

"They said that the massacre was false. That it didn't exist. This is not possible as my knife scars are still there," she told AFP, pointing to her back and shoulder, her eyes glistening with tears.

-- 'Safeguarding history' --

The two Asian powers are now the world's second- and third-biggest economies and have developed deep trade ties, but the weight of history bears heavy on their relationship.

China sees itself as having been humiliated for decades by Japanese imperialists, and earlier this year a wave of anti-Japanese demonstrations broke out across the country, triggered by Tokyo's nationalisation of disputed East China Sea islands.

Japanese firms shut or scaled back production and Chinese consumers shunned Japanese brands, while US Defense Secretary Leon Panetta warned of the risks of escalation.

Some outside historians believe the Nanjing Massacre was an intentional attempt to terrorise China into total surrender, while others argue that, drained by months of combat, the soldiers sought to claim the "spoils of victory".

"Across China people are still bitter over what happened in Nanjing and during the invasion," said Wang Weixing, deputy director of the Institute of History Studies of Jiangsu Provincial Academy of Social Science.

"It is now 75 years since the massacre, but the Japanese refuse to recognise their history."

China accuses Japan of glossing over its wartime past in some school textbooks, and reacts with fury every time a leading Japanese politician visits the Yasukuni shrine in Tokyo, where the souls of the country's war dead are enshrined including 14 Class A war criminals, among them Iwane Matsui, commander of Japanese forces at Nanjing, who was executed after the war.

But Chinese dissidents say Beijing nurtures anti-Japanese sentiment as part of the Communist Party's tightly scripted, historic claim to a legitimate right to rule. Artist Ai Weiwei said this year's protests were "prepared" by Beijing.

Tokyo says it has "deep remorse and heartfelt apology always engraved in mind" over its role in the war.

"Japan candidly acknowledges that during a certain period in its history, Japan, through its colonial rule and aggression, caused tremendous damage and suffering to the people of many countries," says the foreign ministry.

But Xia believes the official position does not go far enough, and wants the Japanese legal system to take a harder stance.

"We should confront the deniers," she said.

In a Japanese court in 2007, she successfully sued Shudo Higashinakano, a professor at Tokyo's Asia University, and his publisher for claiming she was a fraud, winning 4.5 million yen ($55,000 at current rates) in compensation.

In another case involving a second book a court in Nanjing awarded her 1.6 million yuan ($250,000) for defamation.

The publishing house defends both books as "genuine academic research", while Higashinakano has told AFP that the figure of 300,000 deaths was a claim "politically motivated by the Chinese Communist Party".

Xia's lawyers are seeking to have a Tokyo court enforce the Nanjing ruling.

"If it is accepted, this will deliver a strong message to the right-wing Japanese massacre deniers," said Tan Zhen, of Jiangsu FD Yongheng law firm.

"This will have great significance. It is about safeguarding history and upholding justice."