Shinichi Nishimiya, second right, at a forum on economic cooperation between Japan, China and South Korea last year. (File photo/Xinhua)

Japan's newly appointed ambassador to China, Shinichi Nishimiya, fell unconscious on a street in Tokyo on Thursday morning, police said, adding that the sudden faint was caused by illness.

Nishimiya's appointment had just been approved by the government on Tuesday to replace the current envoy Uichiro Niwa at a time when the two countries are embroiled in a dispute over a group of islands in the East China Sea, local media reported.

A passerby saw the 60-year-old Nishimiya suddenly faint on a street in Tokyo's Shibuya ward. Nishimiya was promptly taken to hospital, said police.

As deputy foreign minister in charge of economic affairs, Nishimiya had until recently been making arrangements with other countries in relation to the recently concluded summit of the Asia-Pacific Economic Cooperation forum in Vladivostok, Russia, said local media.

A newly appointed ambassador usually begins work in the designated country within 40 days of the appointment after being briefed by his or her predecessor in Japan, according to the Japanese foreign ministry.