TOKYO: Candidates to become Japan's next prime minister all said they would have better policies to fight the pandemic and reduce the income gap during television debates on Friday, but they were split on diversity issues from same-sex marriage to married couples having separate surnames.

Whoever wins the Liberal Democratic Party presidency on Sept. 29 will become prime minister because of the LDP's majority in the lower house of parliament, and campaigning began in earnest on Friday with a series of televised debates.

Widely seen as the leading contender, vaccine minister Taro Kono, 58, recently veered from mainstream thinking in the conservative party by saying he favours the introduction of same-sex marriage, and during a debate broadcast by TV Asahi, he asked his main contender about his stance on the issue.

Former foreign minister Fumio Kishida, 64, answered by saying he had "not reach to the point of accepting same-sex marriage".

The two other candidates in the race are both women; Seiko Noda, a 61-year-old former gender equality minister, and Sanae Takaichi, 60, an ultra-conservative former internal affairs minister.

While they are not seen as frontrunners the contest is still regarded as unpredictable, and if either were to pull off a surprise win they would become Japan's first female prime minister.

The four candidates will line up for another televised debate on Saturday as they battle to expand support in a party that has suffered a sharp drop in approval ratings due to the handling of the pandemic under Prime Minister Yoshihide Suga's leadership.

Among the more divisive issues separating the candidates is whether to allow married couples to have separate surnames.

Advocates for women, including lawmakers across the political spectrum want women to be able to choose which name they use, but it is not possible under Japanese law.

Takaichi, the more conservative of the two female candidates, said in a debate on Fuji TV that the country should continue the existing system in order to avoid confusion among couples, and their children, with different family names.

The two male candidates adopted a different stance. Kono supports allowing married couples to have different surnames, while Kishida said the public's opinion should be understood before parliament decides.