Voters in Japan are headed to polling stations to elect 125 lawmakers to the Upper House of parliament, in a crucial test for the minority ruling coalition of Prime Minister Shigeru Ishiba.

More than 104 million Japanese are eligible to cast ballots to elect legislators in the House of Councillors from 519 candidates.

Just 75 constituency seats are contested, while the remaining 50 will be elected through proportional representation.

The polls will close at 8 pm (1100GMT), and the results are expected late on Sunday.

A record 21.4 million people had cast votes early by Friday, making up 20.58 percent of all voters, according to Nippon News.

The ruling coalition, comprising Ishiba's Liberal Democratic Party (LDP) and its junior partner Komeito, currently holds 75 seats, but to maintain a majority in the Upper House, it needs to win at least 50 seats from the 125 up for grabs.

Opinion polls suggest Ishiba's LDP and coalition partner Komeito may fall short of the 50 seats needed to retain control of the 248-seat Upper House of parliament in an election where half the seats are up for grabs.

The last time the LDP lost its majority in the Upper House was 2007.

The election is taking place under the spotlight of key issues, including rising prices, regional security, ties with the US, foreign policy, as well as the future of the country's strained social security system.​​​​​​​ In his last day efforts to shore up support for his party, Ishiba told voters: "If politicians only care about what happens now and themselves, this country will cease to exist."

"We must protect Japan whatever it takes because the next six years are going to be the most difficult ones for Japan and the world," he said in Tokyo.