A girl slips her grandmother’s vote into a ballot box at a polling station in Tokyo on Sunday. (Reuters)

Tokyo, Sept. 11 (Reuters): Japanese Prime Minister Junichiro Koizumi’s long-ruling party won a landslide victory in today’s election for parliament’s lower house, TV exit polls showed, a stunning win that will tighten the US ally’s grip on power and give him a broad mandate for market-friendly reform.

An exit poll by public broadcaster NHK showed the Liberal Democratic Party, which has been governing in coalition, would win between 285 and 325 seats in the 480-seat chamber. That represents a striking victory for Koizumi, a media-savvy maverick who gambled his career in a populist appeal to voters to back his plan to privatise Japan’s postal system, a financial services giant that includes a postal savings bank and insurance business with a combined $3 trillion in assets.

“We asked whether the public thinks Koizumi’s structural reforms symbolised by privatisation of the three postal services should be pushed forward or stopped,” said LDP executive Shinzo Abe after the exit poll results.

“I think we received wide support from the public on this point,” added Abe, often tipped to succeed Koizumi when the Prime Minister’s term as LDP president expires next September.

NHK, whose findings were in line with those of private broadcasters, also forecast that the LDP and its partner, the New Komeito party, would win a combined total of between 313 and 361 seats, allowing them to dominate the powerful lower chamber.

The 63-year-old Koizumi, a telegenic veteran with an aptitude for punchy slogans but a mixed record on implementing change, called the election after LDP lawmakers helped the opposition defeat bills to privatise Japan Post in the upper house.

Koizumi’s shock decision to strip LDP rebels of party backing and send what media called “assassin” candidates to challenge the “traitors” grabbed the limelight, making the election as much a referendum on Koizumi himself as on his policies.

A victory for Koizumi’s coalition will please Washington, where he is seen as a staunch friend for backing the US-led war on Iraq, and will be welcomed by investors in Japanese financial markets, who want reform to stay on track.

But there will be little cheering in China and South Korea. Ties with both neighbours, victims of Japan’s past militarism, have chilled since Koizumi took office in 2001 due to perceptions of rising Japanese nationalism.

NHK’s exit poll showed the opposition Democratic Party taking only between 84 and 127 seats, a sharp defeat that was likely to raise questions about the future of a two-party system in Japan, where the LDP has ruled for most of the past five decades.