The documents, handwritten by Japanese tried and convicted by military courts in China after the war, are being released online one a day for 45 days by the State Archives Administration (SAA), it said in a statement on its website.
In the first, dated 1954 and 38 pages long, Keiku Suzuki, described as a lieutenant general and commander of Japan's 117th Division, admitted ordering a Colonel Taisuke to "burn down the houses of about 800 households and slaughter 1,000 Chinese peasants in a mop-up operation" in the Tangshan area, according to the official translation.
Among a litany of other crimes with a total toll in the thousands, he also confessed that he "cruelly killed 235 Chinese peasants seeking refuge in a village near Lujiayu (cutting open the bellies of pregnant women among them)".
He also "ordered the Epidemic Prevention and Water Supply Squad to spread cholera virus in three or four villages".
The document, which is littered with descriptions of "Japanese imperialists", appeared to have been written by someone with native-level command of Japanese, said one Japanese journalist who saw it.
However, some of the sentences were very long and contained multiple clauses, possibly indicating it had gone through several drafts.
It was not clear whether Suzuki's or the other yet-to-be-published confessions -- all of them relating to 45 war criminals put on trial in China in 1956 -- were previously publicly available.
- 'Heinous crimes' -
Suzuki was held by Soviet forces at the end of the conflict and transferred to Chinese custody in 1950, earlier Chinese documents said, adding that he was sentenced to 20 years in prison by the court and released in 1963.
The publication of the confessions comes as Tokyo and Beijing are at odds over a territorial dispute in the East China Sea, and as Beijing has argued that a reinterpretation of Japan's pacifist constitution could open the door to remilitarisation of a country it considers insufficiently penitent for its actions in World War II.
China regularly accuses Japan of failing to face up to its history of aggression in Asia, criticism that has intensified during the term of Prime Minister Shinzo Abe, who won a democratic election in December 2012 and has advocated a more muscular defence and foreign policy stance.
Historians concur that Japan was guilty of numerous atrocities in China, including the Nanjing Massacre in 1937 and germ warfare and other experiments conducted by the infamous Unit 731 on live Chinese captives.
While China is quick to remind Japan of past wrongs, it has been far less willing to recognise the role of the ruling Communist Party in domestic disasters such as Mao Zedong's Great Leap Forward and the ensuing famine that killed tens of millions of people.
Beijing has never allowed a full historical reckoning of the Cultural Revolution of 1966-76 or the 1989 Tiananmen Square killings.
China was outraged in December last year when Abe visited Tokyo's Yasukuni Shrine, where the souls of Japan's war dead, including several high-level officials executed for war crimes after World War II, are enshrined.
"These archives are hard evidence of the heinous crimes committed by Japanese imperialism against the Chinese," the SAA's deputy director Li Minghua was quoted as saying by the official Xinhua news agency.
"Japanese Prime Minister Shinzo Abe, disregarding historical justice and human conscience, has been openly talking black into white, misleading the public, and beautifying Japanese aggression and its colonial history since he took office," Li said.
The SAA said the documents were being released to mark the 77th anniversary Monday of the Marco Polo Bridge incident.
The clash between Chinese and Japanese troops near Beijing is commemorated as the start of what is known in China as the War of Resistance Against Japanese Aggression, which ended with Tokyo's World War II defeat in 1945.