Official campaigning kicked off Thursday for two Upper House by-elections to be held Oct. 25, the first Diet races since the launch of Prime Minister Yukio Hatoyama's administration.

His Democratic Party of Japan will be squaring off against the Liberal Democratic Party in Kanagawa and Shizuoka prefectures over two seats in the 242-member Upper House, where the DPJ coalition with the Social Democratic Party and Kokumin Shinto (People's New Party) holds a small majority.

The stakes are high because if the DPJ wins both by-elections, the party, together with others forming a parliamentary group in the chamber, will reach just one seat shy of a majority on its own.