Chinese Prime Minister Wen Jiabao has used a landmark address to the Japanese parliament, the Diet, to urge Japan to face up to its World War II actions.
It was the first time a Chinese premier had addressed the Diet
In what was the first ever Diet address by a Chinese premier, he said Japan's invasions in the 1930s and 40s had caused China's people tremendous pain.
And he called for Japanese apologies to be matched by concrete actions.
However, he said just a few militarist leaders were to blame and that most Japanese people were also war victims.
Japan and China have been at odds in recent years over Japan's World War II aggression, and China has often accused Japan of not fully atoning for its actions.
Mr Wen's visit to Japan - the first in seven years by a Chinese premier - is being seen as an important step to get over the past and improve ties.
His Japanese counterpart, Shinzo Abe, visited Beijing in October.
History: Japan's neighbours often think it has not done enough to atone for wartime atrocities
Trade: Bilateral trade is growing strongly
North Korea: Japan often takes a tougher stance than China over the nuclear issue
East China Sea: Beijing and Tokyo disagree over the boundary between their exclusive economic zones
Security: Japan wants to revise is pacifist constitution, which concerns China. China's military expansion concerns Japan
Mr Wen began his speech by stressing that he wanted to promote friendship and co-operation between China and Japan, but he focused on the two countries' difficulties over their shared history for much of his speech.
"Japan's invasions caused tremendous damage to the Chinese," Mr Wen said. "The deep scars left in the hearts of the Chinese people cannot be described."
The BBC's Chris Hogg in Tokyo says some commentators in Japan have interpreted that as a warning to Japan's prime minister, Mr Abe, not to visit the Yasukuni shrine honouring its war dead, which the Chinese believe glorifies militarism.
The last Japanese Prime Minister, Junichiro Koizumi, visited the shrine many times as leader, leading the Chinese to refuse to hold bilateral meetings with him.
Mr Wen was positive though about the prospects for the two countries' future relationship, our correspondent says.
"The Chinese people want to exist in friendship with the Japanese people," he said, despite the "calamity" of Japan's World War II invasion of China.
Mr Wen said that "to reflect on history is not to dwell on hard feelings but to remember and learn from the past to open a better future".
Mr Wen also had some strong words on the issue of Taiwan, whose bid for independence from China has found some support in Japan.
He reiterated China's position that it would never tolerate Taiwanese independence, but said he would strive to resolve the position peacefully.
Japan and China both have claims over gas deposits
"We hope that Japan can understand the highly sensitive nature of the Taiwan issue, abide by its pledges and handle the issue prudently," he said.
He also said he hoped China and Japan could find a peaceful solution to their differences over who owns oil and gas reserves in the East China Sea and said that economic development is an opportunity not a threat.
The visit has started well, our correspondent says, with agreements signed on sharing technology to help save energy and to address environmental issues like climate change and China has agreed to resume imports of Japanese rice.
But several difficult issues remain, including the dispute over who owns oil and gas reserves buried under the East China Sea.
Japan accuses China of being secretive about its rapidly growing defence budget, while Beijing is wary of plans to revise Japan's pacifist constitution to make it easier to deploy troops.
Mr Wen is expected to meet the emperor and empress of Japan at the Imperial Palace later on Thursday before lunching with business leaders.
In the evening he will attend a reception to mark 35 years since the re-establishment of diplomatic ties between Tokyo and Beijing.