Japanese Prime Minister Shigeru Ishiba's ruling coalition fell short of his declared "victory line" of a majority in snap parliamentary elections, media projections showed Monday.

AFP examines the options now for the Liberal Democratic Party (LDP) after its worst result since 2009, and the prospects for its bruised leader Ishiba, who only took office on October 1.

- Why the big loss? -

Fiercely critical of former prime minister Shinzo Abe and his brand of establishment politics, Ishiba has long played on his relative popularity with voters as the LDP's "intraparty foe".

But while this won him the party leadership, in the election citizens were more interested in punishing the LDP over a scandal that saw party members pocket money from fund-raisers.

That the main opposition Constitutional Democratic Party (CDP) recently elected moderately conservative former prime minister Yoshihiko Noda as leader also didn't help.

Briefly in office between 2011 and 2012, and known for his "realistic" stance, "I think the majority of Japanese people trust Noda", said Masato Kamikubo, a politics professor at Ritsumeikan University.

"He is a very stable politician", Kamikubo said.

While the LDP's seats as projected by public broadcaster NHK tumbled to 191, from 259 seats at the last election, the CDP's tally soared to 148 from 96.

Komeito, the LDP's coalition partner, slipped to 24 from 32, with new party chief Keiichi Ishii losing his seat.

- Could the opposition form a government? -

This is tricky given the fragmented opposition, and memories of its tumultuous rule between 2009 and 2012, analysts say.

"The possibility of a handover of power to the opposition isn't zero, but there are far too many opposition parties for any of them to reach a majority," said Yu Uchiyama, a political science professor at the University of Tokyo.

Policy differences and past fallings-out continue to divide and hobble opposition parties, from communists to the liberal CDP, the centrist Democratic Party for the People (DPP) and the "reformist conservative" Japan Innovation Party.

- Can Ishiba find new partners? -

The prime minister has his work cut out to make it happen.

On the campaign trail, CDP leader Noda said it would be "impossible" to join forces with the LDP, having been part of previous no-confidence votes.

The Japan Innovation Party also remains unconvinced, with its head Nobuyuki Baba dismissing a tie-up with the LDP in its current scandal-tainted state as "impossible".

The centrist DPP, too, denied it would sign up for the coalition.

But its leader, Yuichiro Tamaki, left open the possibility of a "partial coalition" where it can offer some flexibility on individual policies it has an affinity with.

- What about Ishiba's future? -

Ishiba will likely therefore have to resort to heading a minority administration, seeking support from other parties on a case-by-case basis.

But this is likely to destabilise Ishiba's nascent power base, and leave him susceptible to challenges from within his own party.

Speculation is growing that Ishiba may be forced to resign to take responsibility for the debacle -- becoming the shortest-serving prime minister in Japan's post-war history.

In a nuanced denial of this prospect, though, Ishiba on Sunday night answered in the affirmative when asked by a reporter whether the prime minister intends to follow through on his duties.

"If the ruling coalition or even just the LDP loses its majority, Ishiba will face harsh criticism from party members", Yosuke Sunahara of Kobe University told AFP before Sunday.

But at the same time, the ruling coalition's loss of a majority in the Lower House only goes to lay bare public disenchantment with the political funding scandal.

So if "Ishiba is ousted while the party tries to gloss over the issue, public backlash against the LDP will intensify," Sunahara said.

"This makes it difficult for Ishiba's rivals within the party to criticise him."