Japanese athletes have been told not to wear official tracksuits when walking around Nanjing during the Summer Youth Olympic Games to avoid any possible attack.
The Japanese Olympic Committee (JOC) is also reportedly urging its 78 athletes to don face masks to protect themselves from pollution.
Relations between China and Japan are poor, and JOC Executive Board member Yosuke Fujiwara - who heads the delegation travelling to the Chinese city - has issued the directive.
"When they are outside we want them to be aware that it might not be totally safe," Fujiwara told Kyodo news agency.
"In the Athletes' Village we want them to wear the official Japan tracksuit, but in the city normal clothes are fine."
Explaining the apparent fear of an attack on Japanese athletes, he added: "You can get random attacks on the street in Japan too."
Anti-Japanese sentiment is particularly high in Nanjing, where between 50,000 and 300,000 people were killed in 1937 as Japanese troops invaded the city.
It became known as the Nanjing Massacre.
Bad feeling between the two nations has previously boiled over in the sporting arena.
In the 2004 Asian Cup football final between China and Japan in Beijing, Chinese fans rioted and burned Japanese flags after their opponents controversially won 3-1.
But despite concerns, the JOC is not suggesting athletes stay away from exploring the city.
"We think it's better for the athletes to feel the atmosphere in the city from their own perspective," Fujiwara said:
The Japanese team is due to arrive in Nanjing on Wednesday (August 13) for the Games, due to take place from August 16 to 28.
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