TOKYO: A crowded race kicked off Wednesday to be Japan's next prime minister, with front-runner Taro Aso casting himself as the best person to fight a resurgent opposition in upcoming general elections.

Five lawmakers submitted papers with the Liberal Democratic Party (LDP) by Wednesday's deadline to run in the September 22 ballot the most since the long-dominant party started its current election system.

Aso a hawkish former foreign minister seen as cool on free-market reforms was flanked by supporters at his kick-off rally at the LDP headquarters.

"With general elections due to be held within a year, the crucial issue is who will fight the opposition," said Aso, the LDP secretary general who is making his fourth attempt for the top job.

"We will have to make an appeal to voters in the entire nation that this country has underlying strengths," he said. "I hereby renew my determination to take the lead."

The next prime minister must call elections by September 2009 but some LDP lawmakers want snap polls to take advantage of the initial popularity of the new leader.

A weekend poll showed the LDP with a narrow edge over the opposition among voters, whose support for the ruling party has grown since Fukuda resigned.

Aso leads in polls on who would be the best prime minister, outpacing his LDP rivals and opposition leader Ichiro Ozawa. Fukuda abruptly quit last week after months of dismal approval ratings as Japan's economy, the world's second largest, falters. Fukuda also came under intense criticism for raising medical costs on elderly people.

The opposition last year seized control of one house of parliament and is hopeful it can win a landmark general election victory against the LDP, which has been in power for all but 10 months since 1955.

Aso, 67, has promised to focus on stimulating the economy, even by cutting taxes, rather than on trimming Japan's public debt which is the highest among rich nations.

Former justice minister Kunio Hatoyama said Aso a popular stump-speaker with a love of pop culture would be "the most lively prime minister in history" and serve the LDP best in general elections.

"We have gathered here to say goodbye to a gloomy and spineless Japan," Hatoyama said by Aso's side.

Aso hopes to win a majority in the first round of voting so his opponents do not rally around one of the other candidates. They include former defence minister Yuriko Koike, who is vying to be Japan's first female leader.

"The LDP is changing!" Koike told supporters at a rally where she handed out colourful fliers and wristbands.

"I am the evidence that the LDP is changing," she said to applause from a few dozen party members, many of them women. "I am running in the presidential election of the LDP, which has such a long history and tradition."

Other candidates include Kaoru Yosano, a staunch advocate of fiscal discipline who supports tax hikes.

He told supporters he will not hesitate to talk straight on his beliefs.

"I will speak out on my real, strongly held opinions," said the 70-year-old political veteran.

Another candidate, Shigeru Ishiba, a former defence minister who spearheaded Japan's landmark military deployment to Iraq, said he wanted to put national security at the forefront of the race.

"The fight against terrorism has reached its most critical stage," he said. "National security and people's everyday lives must be debated at the same level."

The other candidate is Nobuteru Ishihara, 51, an economic reformist and son of Tokyo's outspoken governor who says he represents a new generation within the party.