Relations between Asia's two biggest economies have faltered badly, with emotions running high on the streets and also out at sea where two Japanese activists landed on an island at the centre of the dispute.
China reacted swiftly to the news of the landing, which risked inflaming a crisis that already ranks as China's worst outbreak of anti-Japan sentiment in decades. Beijing described the landing as provocative, lodged a complaint with Tokyo and said it reserved the right to take further action.
The dispute over the uninhabited group of islands in the East China Sea known as the Senkaku in Japan and Diaoyu in China led to another day of protests that were smothered by a heavy blanket of security.
Japanese businesses shut hundreds of stores and factories across China and Japan's embassy in Beijing again came under siege by protesters hurling water bottles, waving Chinese flags, and chanting anti-Japan slogans evoking war-time enmity. Japanese PM Yoshihiko Noda urged Beijing again to protect Japanese citizens in China.
Today is our day of shame, said a Beijing protester, Wei Libing, a waiter in his 40s. Japan invaded China on this date.
Sino-Japanese ties have long been plagued by China's bitter memories of Japan's military aggression in the 1930s and 1940s and present rivalry over resources the islands are believed to be surrounded by energy-rich waters.
For China, Tuesday marks the day Japan began its occupation of parts of mainland China in 1931.