TOKYO — Japan’s conservative Liberal Democratic Party returned to power in a landslide election victory Sunday after three years in opposition, according to unofficial results, signaling a rightward shift in the government that could further heighten tensions with China, a key economic partner as well as rival.
The win means the hawkish former Prime Minister Shinzo Abe will get a second chance to lead the nation after a one-year stint in 2006-2007. He would be Japan’s seventh prime minister in 6½ years.
In the first election since the March 11, 2011, earthquake, tsunami, and nuclear disasters, atomic energy ended up not being a major election issue even though polls show 80 percent of Japanese want to phase out nuclear power.
Public broadcaster NHK’s tally showed that the Liberal Democrats, who ruled Japan for most of the post-World War II era until it was dumped in 2009, won 294 seats in the 480-seat lower house of Parliament. Official results were not expected until Monday.
The Liberal Democrats, the most pronuclear-power party, had 118 seats before the election. A new, staunchly antinuclear-power party won just nine seats.
Economic concerns won out, said Kazuhisa Kawakami, a political science professor at Meiji Gakuin University.
‘‘We need to prioritize the economy, especially since we are an island nation,’’ he said. ‘‘We’re not like Germany. We can’t just get energy from other countries in a pinch.’’
The results were a sharp rebuke for Prime Minister Yoshihiko Noda’s ruling Democratic Party of Japan, reflecting widespread unhappiness with its failure to keep campaign promises and get the stagnant economy going during its three years in power.
Calling the results severe, Noda said he was stepping down as party chief to take responsibility for the defeat. ‘‘I apologize deeply for our failure to achieve results,’’ he said
The Democratic Party of Japan won in a landslide three years ago but won only 57 seats, compared with 230 seats before Sunday’s election,