Japanese voters swept to power an untested centre-left party on Sunday in an electoral avalanche that ended more than half a century of almost unbroken conservative rule, according to exit polls.
The win by the Democratic Party of Japan (DPJ) ends a half-century of almost unbroken rule by the Liberal Democratic Party (LDP) and breaks a deadlock in parliament.
Media projections showed the Democrats set for a landslide win, possibly taking two-thirds of the seats in parliament's powerful 480-member lower house.
"I am thankful for the support shown by the public," said Democratic Party leader Yukio Hatoyama, who is expected to take over as prime minister in about two weeks once the new parliament or Diet convenes.
"Looking at the situation so far, I feel extremely grateful," he added, stopping short of a full claim of victory. "I think that the public has felt an extreme sense of frustration with the government of the ruling party."
"This is about the end of the post-war political system in Japan," said Gerry Curtis, a Japanese expert at Columbia University.
Media exit polls showed the Democratic Party had won around 320 lower house seats -- almost triple its 115 before the election. The LDP slumped to just over 100 seats from 300.
Aso said he took responsibility for the defeat, adding an LDP leadership race to pick a successor should be held soon.
Hatoyama, a US-trained engineering scholar, 62, the wealthy grandson of a former prime minister, campaigned on a promise of change and people-centred politics against the business-friendly LDP, headed by fellow political blueblood Aso.
Recalling US President Barack Obama's election victory last year, Hatoyama asked voters in a final campaign speech on Saturday at a Tokyo railway station: "Why can't we do what the United States could do?"
"I don't like what's going on now in this country. Things have to change," said Kazuya Tsuda, a 78-year-old retired doctor in Tokyo who voted for the Democratic Party.
The DPJ already controls the upper house with the support of smaller parties, including the Social Democrats. A two-thirds majority in the lower house would give the party the numbers to push through legislation.
"I don't think the LDP can change anything," said Ryoji Kawakita, a 63-year-old white-collar worker who voted for the Democratic Party. "I think, even though it will be difficult, the DPJ might be able to achieve change because they have the will."
"It seems like the Democrats are just saying what the people want to hear, but I'm not sure they can follow through on these promises," said Taku Yamada, a 30-year-old health-care industry worker who voted for the LDP.
"The Democrats have good policy proposals. But I'm not sure all of them are really achievable. If we have a handover of power, everything has to start from scratch and it would be ordinary people who end up suffering," said Tomiko Machida, a 75-year-old pensioner who voted for the LDP.
"The new government needs to do something about unemployment. I see many young people idling around doing nothing."
A new leader is expected to attend a series of international meetings including the U.N. General Assembly and a G20 summit in Pittsburgh in September.
The party wants to forge a diplomatic stance more independent of the United States and build better ties with Asia.
A key challenge for the next government will be managing ties with China, forecast to overtake Japan as the world's second-biggest economy next year.