Wu Dawei arrives before a meeting with South Korean Foreign Minister Yun Byung-Se
North Korea marks several major anniversaries this month and often marks the occasions with major tests of military hardware.
The possibility of US military action against North Korea in response to such a test emerged as an option following last week's US strikes against Syria.
It was further fuelled by comments from US President Donald Trump's top aides on the weekend.
Yun Byung-Se and Wu Dawei shake hands
It probably is not realistic for the US to attack North Korea
Japanese defence ministry source
In Tokyo, the feasibility of US military action was downplayed, while South Korea said the focus remained on deterrence and readiness.
"It probably is not realistic for the US to attack North Korea," a Japanese defence ministry source said.
"If America says it is going to attack, both Japan and South Korea will probably put a stop to it," said the source who declined to be identified.
South Korea said the focus remained on deterrence and readiness
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US Secretary of State Rex Tillerson said the US military strike against Syria over its alleged use of chemical weapons was a warning to other countries including North Korea that "a response is likely" if they pose a danger.
"President Xi clearly understands, and I think agrees, that the situation has intensified and has reached a certain level of threat that action has to be taken," Secretary Tillerson said on CBS's Face the Nation.
Mr Wu is expected to discuss the North's nuclear issue with Yun Byung-Se
China's Special Representative for Korean Peninsula Affairs Wu Dawei is expected to discuss the North's nuclear issue with his South Korean counterpart, according to the South Korean foreign ministry.
Mr Wu's trip comes after Trump and President Xi met in Florida, where President Trump pressed his counterpart to do more to curb North Korea's nuclear programme.