China has been holding ceremonies to mark the 70th anniversary of the Nanjing massacre.
The people of Nanjing paused to remember those killed
Survivors attended the reopening of a memorial hall, built to remember an act that has come to symbolise imperial Japanese aggression in China.
Japanese soldiers carried out the killings in a six-week period after Nanjing was captured in December 1937.
Beijing says 300,000 Chinese civilians were killed, but some Japanese historians dispute this figure.
In the city, air sirens were sounded as people paused in silence to remember the victims.
The memorial hall which details the violence has been reopened after two years of renovations.
Its purpose is "to better preserve history... to never forget the past... to treasure peace and open the way to the future", Xu Zhonglin, a provincial Communist Party chief, told the French news agency AFP.
Alongside the officials and thousands of residents attending the ceremony were a number of survivors.
Twenty-five-year-old Xia Lu came with her grandmother, who lived through the massacre.
"Her father was killed by Japanese in 1937 and then her mother had no ability to raise her children, so she sent her children to other families," she told the BBC.
One elderly woman described how she had been five years old when a Japanese soldier gouged out her eyes with a bayonet.
The BBC's Michael Bristow, in Nanjing, says the anniversary is more than a commemoration of past events, and remains fresh in the minds of many.
He says that is partly because many Chinese people see history as a guide to the future - but also because of continuing research into the atrocities.
A new monument has just been unveiled to mark a previously unknown incident during the massacre in which 1,300 Chinese people died.
That story came to light only because a Japanese researcher persuaded former soldiers to tell their stories.
In Japan, the anniversary of the assault on Nanjing is not being commemorated officially.
One of the Chinese people attending the ceremony, Chen Fubao, now aged 75, had a message for the country whose forces carried out the slaughter.
Japan was not officially marking the anniversary
Holding a photograph of his father, who was killed in the violence, Mr Chen told Reuters: "We hope that the Japanese government, especially those in the nationalist factions, will admit the truth in history and learn from the Germans.
"They should not cover up their crimes anymore."
Japanese prime ministers have apologised for the country's former militarism, but, according to the BBC's Chris Hogg in Tokyo, there are fringe elements in Japan who get a lot of publicity for their repeated denials that Japan committed atrocities during its military campaigns in Asia.
Some even deny that the events in Nanjing ever took place and, our correspondent says, this frustrates mainstream historians who try to give a more balanced view of what happened during the assault on the city.
Younger Japanese are frustrated, too, that their country is criticised still for events that took place more than half a century ago, he adds.
Many know little about what went on in Nanjing and care even less.