Japanese Prime Minister Sanae Takaichi's Liberal Democratic Party (LDP) won 315 seats in weekend snap elections, giving it a two-thirds majority, official results confirmed on Tuesday.

The outcome is the LDP's best in its history and allows Japan's first woman prime minister to stamp her mark on the country of 123 million people over the next four years.

The LDP's coalition partner, the Japan Innovation Party (JIP), won 36 seats, giving the ruling bloc 351 lawmakers in the 465-member lower house, the internal affairs ministry data showed.

In the last parliament the LDP had only 198 seats while the JIP had 34.

The election also saw the anti-immigration Sanseito party increase its tally to 15 seats from two.

The new Centrist Reform Alliance of the main opposition Constitutional Democratic Party and the LDP's previous partner Komeito suffered a disaster, with their tally collapsing to 49 from 167.

Having a two-thirds majority enables the government to override decisions by the upper house where the coalition is in a minority.

It also gives Takaichi the option of embarking on the complicated task of trying to change the constitution, something she has indicated she wants to do.

"This is the start of a heavy, heavy responsibility to make Japan stronger, more prosperous," Takaichi, 64, said on Monday.

"We believe that the public has shown understanding and sympathy regarding our appeals concerning the urgent need for a major policy shift," she said. (AFP)