TOKYO (AFP) - Japan's main opposition party won a key weekend local poll in a landslide, official figures showed, handing it a significant and much-needed boost ahead of national elections later this year.

"It is very significant that we scored a landslide victory in a major city when a general election is drawing near," Democratic Party of Japan (DPJ) secretary-general Yukio Hatoyama said in a statement.

"We will be fully prepared for the general election to topple the government," he said after Takashi Kawamura won the mayoral election in the central industrial city of Nagoya.

Kawamura, 60, won 514,514 votes against 282,990 votes for runner-up Masahiko Hosokawa, backed by the ruling Liberal Democratic Party and its junior coalition partner, the New Komeito party.

The opposition DPJ has suffered two election defeats in local polls since leader Ichiro Ozawa was hit by a funding scandal last month.

Ozawa, who had been widely tipped as a likely future premier, has seen his popularity slide since, and recent opinion polls have showed public support for Taro Aso's cabinet recovering, fuelling speculation of early elections.

Despite that, pundits have said the general election, which must be held by September, will be the toughest fight yet for the ruling conservative party in its almost unbroken rule of Japan lasting more than half a century.