Moon Jae-in, South Korea's new president, has declared his willingness to visit the nuclear-armed North, moments after taking his oath of office.

Moon, who was declared the winner on Tuesday of the presidential election, said he will "sincerely negotiate" with the United States, South Korea's chief ally, and China, South Korea's top trading partner, over the contentious deployment of the US anti-missile system THAAD.

The missile defence system has angered China, which says its powerful radars allow the US to spy on its own military operations.

Moon, 64, begins his five-year term as president after Park Geun-hye was toppled and indicted for corruption.

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Voter turnout was at its highest in 20 years, with Moon taking 41.1 percent of the vote - roughly 13.4 million ballots - according to the National Election Commission (NEC).

Speaking during his formal oath-taking ceremony on Wednesday, Moon pledged to work for peace on the Korean Peninsula amid growing worry over the North's expanding nuclear weapons and missiles programme.

"I am willing to go anywhere for the peace of the Korean Peninsula," Moon said.

"If needed, I will fly immediately to Washington. I will go to Beijing and I will go to Tokyo. If the conditions shape up, I will go to Pyongyang."

Al Jazeera's Rob McBride, reporting from Seoul, said Moon laid out the priorities of his presidency as he was sworn in.

"From the start of his speech, Moon spoke of the burden that now rests on his shoulders following the recent turmoil and impeachment of his predecessor," he said.

"Moon spoke of the strength of the Korean people in overcoming these hurdles ... and was at his most impassioned when he spoke for the need of peace in the Korean Peninsula.

"That message of dialogue with the North, however, jars with the US, which has embarked on a more hardline approach. But when it came to the relationship with Washington, he also spoke of while they have had disagreements over the THAAD, their alliance would remain strong."

Rising tensions

North Korea recently tested a ballistic missile and claims it is close to perfecting an intercontinental ballistic missile and nuclear warhead that could attack the US mainland.

Tensions between North Korea and the US go back to the 1950-53 Korean War, which ended in an armistice, not a peace treaty.

But tensions have been rising rapidly since US President Donald Trump took office in January.

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Trump has threatened that if China is not willing to do more to squeeze the North over its nuclear and missile programmes, the US might take matters into its own hands.

Many analysts believe at its current pace of testing, North Korea could reach that potential turning point within a few years - under Trump's watch as president.

The North conducted two nuclear weapon tests last year alone. The first was of what it claims was a hydrogen bomb and the second was its most powerful ever.