Japan's next prime minister, Yukio Hatoyama, set about planning his new government this morning, hours after his party's overwhelming election victory over the Liberal Democrats. Mr Hatoyama gave little away about his plans for senior posts in the new government, as he held meetings with senior members of his Democratic Party of Japan (DPJ). It's taken a long time, but we have at last reached the starting line," he said at a morning news conference. "This is by no means the destination. At long last we are able to move politics, to create a new kind of politics that will fulfil the expectations of the people." Japan woke to a new political era after the DPJ won 308 out of 480 seats in the lower house of the Japanese Diet, close to three times the number it had at the last election. The Liberal Democratic Party (LDP), which governed Japan almost without interruption for 54 years, went from 300 seats to 119. Its leader, the outgoing prime minister, Taro Aso, confirmed that he would step down as party leader. There will now be a hiatus of as long as two weeks, while Mr Hatoyama prepares to be formally elected prime minister by a special session of parliament in the middle of next month. The new Diet will contain 158 first-time politicians, 90 per cent of them members of the DPJ, and the youngest of them 27 years old. The average age of those elected yesterday is 52, or 49 for members of the DPJ. The rump of surviving LDP members have an average age of 57, and almost half of them are so-called "hereditary candidates", who inherited constituency seats from a mother or father. A record 54 MPs are women, 40 of them from the DPJ. Apart from the changes within the Diet, a whole range of institutions, within Japan and abroad, must now establish relationships with an entirely new set of politicians. "We have entered an age where a genuine transition of government is possible for the first time in the post-war history of constitutional politics," Fujio Mitarai, the chairman of Japan's powerful Keidanren business federation, said. The newly arrived US ambassador to Japan, John Roos, promised to work with the new government, which has pledged to pursue a "more equal" relationship with Washington. "The challenges we face are many, but through our partnership our two great democracies will meet them in a spirit of cooperation and friendship," he said. The White House spokesman, Robert Gibbs, said: "As a close friend and ally, the United States awaits the formation of a new Japanese government. "President Obama looks forward to working closely with the new Japanese prime minister on a broad range of global, regional and bilateral issues."