World leaders were in near unison voicing their opposition to North Korea's latest nuclear test Friday and lambasting the country's top official as being reckless in his apparent quest to fine-tune the nation's nuclear program.

South Korea's president seemed to be leading the chorus of disapproval, saying in part that North Korean leader Kim Jong Un's "mental state" is "uncontrollable," Korean news agency Yonhap reported.

"This (Pyongyang's nuclear test) clearly reaffirmed the North Korean regime's recklessness and its obsession with nuclear arms," South Korean President Park Geun-hye said Friday. "Kim Jong-un does not listen to any voice, and this leads us to view Kim Jong-un's mental state as uncontrollable."

Park's view on Kim were pretty much in line with those of other world leaders, including Canadian Prime Minister Justin Trudeau, who called North Korea's most recent nuclear test — its fifth ever, second in eight months and the most powerful of them all — "an unacceptable violation" of United Nations Security Council resolutions.

But it was the neighboring nations to North Korea that seemed to reserve the most vitriol for Friday's nuclear test. 

The chief cabinet secretary of Japan — which all but threatened war after North Korea conducted a test-firing of a ballistic missile that landed in Japan's waters — called the nearby country an "outlaw nation in the neighborhood," the Associated Press reported.

Even China, a key ally of North Korea, condemned the nuclear test for its apparent "disregard" for the international community's opposition.

The policy chief for the European Union issued a statement that comes across as both a condemnation as well as an ultimatum. "There is no alternative," said Federica Mogherini, the High Representative/Vice-President of the EU. "[North Korea] must abide by its obligations and abandon all its nuclear weapons and existing nuclear programmes in a complete, verifiable and irreversible manner."

U.S. President Barack Obama said there would be "serious consequences" for North Korea's actions, according to Reuters, before issuing a formal statement.

"North Korea stands out as the only country to have tested nuclear weapons this century," Obama said. "Today's test, North Korea's second this year, follows an unprecedented campaign of ballistic missile launches, which North Korea claims are intended to serve as delivery vehicles for nuclear weapons targeting the United States and our allies, the Republic of Korea and Japan. As Commander in Chief, I have a responsibility to safeguard the American people and ensure that the United States is leading the international community in responding to this threat and North Korea's other provocations with commensurate resolve and condemnation."

Park is expected to meet Friday with her country's top security and foreign policy officials, likely to devise a planned response to North Korea's provocative nuclear test, Yonhap reported.