President Donald Trump conceded that North Korea was "sort of a nuclear power" as he left the US for Asia on a trip that could include a meeting with Pyongyang's leader Kim Jong-un.

Asked aboard Air Force One about North Korea's demand to be recognized as a nuclear state as a precondition for dialogue with the US, Trump on Friday replied: "Well, I think they are sort of a nuclear power.

"When you say they have to be recognized as a nuclear power, well, they got a lot of nuclear weapons, I'll say that."

Trump is expected in South Korea on Wednesday for the Asia-Pacific Economic Cooperation (APEC) Forum.

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Media reports say officials from his administration have privately discussed setting up a meeting between Trump and North Korean leader Kim, with whom he last held ultimately unsuccessful talks in 2019.

Trump has said he hopes to meet Kim again, possibly this year.

Kim said last month he had "fond memories" of Trump and was open to talks if the US dropped its "delusional" demand that Pyongyang give up its nuclear weapons.

On Friday, South Korea's unification minister Chung Dong-young said he believed there was a "considerable" chance that Trump will meet Kim during his visit to the peninsula next week.

But a senior US official, speaking on condition of anonymity, told reporters in a call Friday that a meeting "is not on the schedule for this trip."

While no official announcements of the duo's meeting have been made, South Korea and the United Nations Command halted tours of the Joint Security Area (JSA) from late October to early November.

Minister Chung said North Koreans have been spotted "sprucing up" areas near the JSA for the first time this year.