Prime Minister Shinzo Abe's lead in next month's election has shrunk as the popular Tokyo governor pushes to unite opposition forces, a survey by Japan's top-selling daily indicated Saturday. 

Thirty-four percent of Japanese plan to vote for Abe's conservative Liberal Democratic Party (LDP) while 19 percent favour a party formed this week by Tokyo Governor Yuriko Koike, according to the poll in the Yomiuri Shimbun.

It also showed one quarter of those polled were still undecided on how vote in the October 22 election.

The findings suggest Abe's path to victory may not be as easy as earlier believed.

The poll was taken on Thursday and Friday, right after the main opposition Democratic Party made a surprise move to join forces with Koike's newborn "Party of Hope".

Koike is also talking with smaller opposition groups to explore possibilities of cooperation.

A survey in the leading business daily Nikkei last weekend had showed 44 percent of Japanese plan to vote for the LDP while only eight percent favoured the Democratic Party.

Abe on Monday called the snap election, seeking a fresh term at the helm of the world's third-largest economy.

He hoped to capitalise on a weak and fractured opposition to sweep back into power, as polls had shown him regaining ground for his hawkish stance on rising tensions with nearby North Korea.

But Koike stole his limelight by launching her party with the criticism that the pace of much-needed reforms under Abe's government is too slow.

The Yomiuri conducted the survey on which party voters plan to cast their ballots for under the proportional representation system.

A total of 465 seats are up for grabs in the lower-house election on October 22, of which 289 are to be elected from single-seat districts and 176 by proportional representation.

Both Yomiuri and Nikkei surveys were telephone polls that covered more than 1,000 eligible voters across the nation.