The Japanese ambassador to China died in a Tokyo hospital after being admitted three days earlier. His death coincides with an escalation in anti-Japanese protests across China over a territorial dispute.

The cause of ambassador Shinichi Nishimiya’s death is currently under investigation, Japan's Ministry of Internal Affairs said. Three days ago, Nishimiya was found unconscious near his Tokyo home after leaving for work.

A second day of demonstrations took place across China against Japan's territorial claim to a group of disputed islands in the East China Sea. China does not recognize Japan's claim to the isles, which are known to the Japanese as 'Senkaku' and as 'Diaoyu' by the Chinese.

In Shenzhen, a city near Hong Kong in southern China, police dispersed thousands of activists with water cannons. And in the eastern city of Qingdou, witnesses reported smoke and flames coming from a factory owned by Japanese electronics manufacturer Panasonic. A Toyota dealership was also damaged in Qingdou, a company spokesperson said.

In response, Japanese Prime Minister Yoshihiko Noda called on the Chinese government to “ensure the security of Japanese citizens,” and decried the recent surge of anti-Japanese demonstrations. “I strongly object to the burning of Japanese flags and the protests,” Noda said on a Japanese talk show broadcast by NHK.

Tensions between the two countries intensified on Friday when six Chinese ships entered Japanese waters near the disputed islands and ignored the Japanese Coast Guard's orders to leave. The move triggered angry protests in hundreds of Chinese cities, some of which were reportedly violent.

A Chinese protester hurls a water bottle during an anti-Japanese protest over the Diaoyu islands issue, known as the Senkaku islands in Japanese, outside the Japanese Embassy in Beijing.(AFP Photo / Goh Chai Hin) ­Chinese para-military police (bottom) shelter behind a barrier as demonstrators continue to throw eggs, rocks and water bottles during an anti-Japanese protest outside the Japanese embassy in Beijing over the Diaoyu islands issue, known as the Senkaku islands in Japanese.(AFP Photo / Mark Ralston) ­Chinese demonstrators carry national flags and portraits of Mao Zedong during a protest over the Diaoyu islands issue, known as the Senkaku islands in Japan, in Wuhan.(AFP Photo / China Out) ­Chinese protesters hurl water bottles during an anti-Japanese protest over the Diaoyu islands issue, known as the Senkaku islands in Japanese, outside the Japanese Embassy in Beijing.(AFP Photo / Goh Chai Hin) ­Chinese protesters hurl water bottles during an anti-Japanese protest over the Diaoyu islands issue, known as the Senkaku islands in Japanese, outside the Japanese Embassy in Beijing.(AFP Photo / Goh Chai Hin) ­Chinese para-military police look at various items through lying on the ground during anti-Japanese protests outside the Japanese embassy in Beijing over the Diaoyu islands issue, known as the Senkaku islands in Japanese.(AFP Photo / Mark Ralston) ­Chinese para-military police walk behind a barrier as demonstrators continue to throw eggs, rocks and water bottles during an anti-Japanese protest outside the Japanese embassy in Beijing over the Diaoyu islands issue, known as the Senkaku islands in Japanese.(AFP Photo / Mark Ralston) ­Chinese demonstrators carry anti-Japan banners and march during a protest over the Diaoyu islands issue, known as the Senkaku islands in Japan, in Wuhan.(AFP Photo / China Out)