Campaigning began for a Japanese upper house election on July 29 that could cost Prime Minister Shinzo Abe his job and usher in a period of policy stagnation if his ruling bloc loses heavily.

Chances that Mr Abe's coalition will keep its upper house majority have dimmed because of mishandling of pension records and a series of scandals and gaffes that cost the Cabinet three ministers, two from resignations and one by suicide.

"The battle starts from here," Mr Abe told a crowd in Tokyo's Akihabara electronics shopping district, a mecca for "otaku" geeks who adore manga comics and anime.

"Will it be reform or moving backwards? Will there be economic growth, or going backwards?" Mr Abe shouted as rain fell.

The LDP and its junior partner, the New Komeito party, need to win a total of 64 seats to keep their majority in the upper house, where half of the 242 seats are up for grabs.

The main opposition Democratic Party is touting the upper house poll as a step towards taking power. "This is the best and last chance to change politics that abandons the weak and abandons the regions," the Democrats' leader, Ichiro Ozawa, told a crowd in western Japan, where he began his party's campaign.

"If you do not give us a majority this time, a change in government in Japan will be impossible," he added.

A loss by the ruling camp would not automatically require Mr Abe to step down, since the lower house picks the Prime Minister.