Japanese Prime Minister Shigeru Ishiba's ruling coalition is at risk of losing its majority in the upper house in Sunday's election, multiple polls showed as voting got underway.
The Liberal Democratic Party (LDP), already in a minority in the lower house since last October's snap election, faces mounting public discontent over inflation, political scandals, and a surge in anti-immigration sentiment.
With only 50 of the 125 contested seats needed to retain control, the LDP and its junior partner Komeito are projected to fall short, according to polls by Kyodo, Yomiuri, and Nikkei.
This would have a drastic impact on Japan's fiscal and political outlook, and comes at a time when Tokyo is struggling to strike a trade deal with the US amid President Donald Trump's tariffs.
Prime Minister's future hangs in balance
This election will also decide the political future of Ishiba.
A major defeat, like last year's, could force his resignation and pave way for a power struggle within the LDP.
Small, opposition parties with anti-establishment messages are likely to erode support from the ruling power.
If the coalition loses both houses, Japan would enter uncharted political territory as the LDP has been in power perpetually since its foundation in 1955, barring a few years in the middle.
Japan's snap election backfires on ruling party
Rise of the 'Japanese First' party
The surge of the right-wing populist Sanseito party is complicating the race.
Once a fringe movement, spreading conspiracy theories about vaccinations and global elites during the COVID-19 pandemic on YouTube, the party is now gaining momentum with its "Japanese First" rhetoric and criticism of immigration, globalism, and foreign capital.
Analysts say Sanseito could win over 10 seats, appealing especially to young male voters.
Its leader, Sohei Kamiya, has drawn comparisons to Trump and Germany's AfD for his anti-establishment stance and social media reach.
On Sunday, a Sanseito candidate's interview by Russia's Sputnik news agency courted controversy and prompt denials of ties to Russia by Kamiya, according to AFP news agency.
The European Union has banned Sputnik along with other Russian state media for "disinformation and information manipulation."
Edited by: Alex Berry