Japan’s benchmark Nikkei 225 index tumbled nearly 5% early Monday after the country’s ruling Liberal Democrats chose Shigeru Ishiba, a former defense minister, as the next prime minister.

Former Defense Minister Shigeru Ishiba, a plain-spoken populist, won leadership of Japan’s ruling Liberal Democratic Party in a runoff vote on Friday.

Japan's incoming prime minister, Shigeru Ishiba, said he wanted to clean up his ruling party, revitalise the economy and see off security threats from powerful neighbours after triumphing in his fifth and what he called final leadership bid on Friday.