TOKYO (AFP) - Japanese teenage athletes at the Youth Olympics starting on Saturday in the Chinese city of Nanjing have been warned not to wear their official tracksuits around town due to safety fears, local media have reported.

Delegation chief Yosuke Fujiwara has told Japan's 78 athletes to wear regular clothes outside the Games venues during the Aug 16-28 event to avoid any attack, with Tokyo-Beijing relations at their lowest level in years.

They will also be encouraged to don face masks to protect themselves from China's notoriously bad air pollution.

"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."

In an apparent attempt to avoid upsetting the Chinese before the second edition of the Youth Games, Fujiwara added: "You can get random attacks on the street in Japan too."

Anti-Japanese resentment runs particularly high in Nanjing, where China says 300,000 people - some estimates are lower - were killed in 1937 as Japanese troops rampaged through the city during their invasion of the mainland. It became known as the Nanjing Massacre, or Rape of Nanking in some quarters.

The killing was the Japanese military's worst atrocity and remains a bitter stain on the two countries' relationship.

Fujiwara's comments came at a time of heightened political tension between Japan and China, which are at odds over claims to islands in the East China Sea and historical grievances tied to Japan's wartime aggression.

Japanese Prime Minister Shinzo Abe's recent decision to relax strict rules governing the country's military has further antagonised Beijing, prompting Fujiwara to issue the warning.

But he insisted that the contestants would still be free to explore the city.

"We think it's better for the athletes to feel the atmosphere in the city from their own perspective," Fujiwara said.

Japanese sports teams and the country's national anthem are frequently booed in China, most notably at the 2004 Asian Cup football final between China and Japan in Beijing which ended in a full-scale riot after Japan's controversial win.

Japan's delegation arrives in Nanjing on Wednesday. It features girls' badminton junior world champion Akane Yamaguchi and Yuto Muramatsu, who won bronze in the men's singles at the Japan Open table tennis earlier this year.

The event is open to athletes aged from 14 to 18. The first Youth Games were held in Singapore four years ago, and the next in 2018 will be in Buenos Aires in Argentina.