NHK's Hiroshima broadcasting station has apologized over a series of Twitter posts it made in the name of wartime residents as part of a history project for young people following criticism that they fanned discrimination against Korean residents.

The apology over the tweets, which were based on residents' diaries, follows the public broadcaster's apology in June over a Twitter video that came under fire for presenting racist stereotypes about black people.

The tweets in question are part of 1945 Hiroshima Timeline, a "what-if" social media project the station launched in March to help younger generations imagine the lives of citizens in the atomic-bombed city during and after World War II.

People demonstrate in front of NHK Hiroshima broadcasting station on Aug. 22, 2020. (Kyodo)

The tweets were based on diaries kept by a 13-year-old boy, a housewife and a newspaper reporter in Hiroshima 75 years ago and presented as if the three people had posted them, using modern language.

However, criticism emerged over tweets made June 16 and Aug. 20 by "Shun," the 13-year-old boy, that touched on Koreans.

In tweets hypothetically posted on Aug. 20, 1945, or five days after Japan's surrender, Shun, while traveling to Saitama from Hiroshima by train, wrote about how a crowd of Koreans forced their way onto a packed train in Osaka by smashing windows and shouting, "We are citizens of a victor country! Get out, (people of) the defeated country!"

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Several Hiroshima citizens held a protest rally outside the broadcasting station on Saturday, saying the tweets could be used to justify discrimination against Koreans.

A 33-year-old woman said the broadcaster "completely lacked awareness about the violent nature of the tweets, and the imagination to see what will happen in current Japanese society where discrimination is rampant if such posts are made."

Supplied photo shows screenshot of NHK Hiroshima bureau's tweets in their "1945 Hiroshima Timeline." (Kyodo)

A 54-year-old man said the tweets "inadvertently contained the message that it is OK to reject Korean residents of Japan because some of them committed violence in the past."

The NHK station initially defended the tweets, saying they were meant to convey the situation at the time and adopted wording from the diary and personal interviews it held with the man who wrote it.

But on Monday, the station admitted that it "had lacked consideration" and offered an apology.

In a statement it posted on its website, it said it "did not pay full consideration to the possible reaction by a modern-day audience" to posts about what a 13-year-old saw and heard during the war and its aftermath.

It also apologized for the implication that the real Shun held negative feelings toward Koreans and still does so now.

The bureau said it will continue with the "1945 Hiroshima Timeline" project, which is aimed at conveying the tragedy of war and of the nuclear attack to younger generations, but provide background information as needed.

In June, NHK apologized over a short animation it used on a weekly news program and posted on Twitter to explain the background to the Black Lives Matter protests in the United States.

The video depicts a muscle-bound black man in a white tank top holding an empty purse and yelling at a fully clothed white man. It was aired as part of a roughly 30-minute show that each week explains world affairs and their implications for Japan.