Dennis Rodman is heading back to North Korea, US broadcaster CNN reports, three years after the eccentric former NBA star last travelled to the reclusive nation and sang Happy Birthday to leader Kim Jong Un.

CNN spotted Rodman at Beijing International Airport but he refused to answer questions.

However, two officials in North Korea confirmed to the broadcaster that Rodman was expected to arrive there.

The reasons for Rodman's trip and its duration are unknown.

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Rodman is one of the only Americans to have met Kim Jong Un and will arrive at a time of high tension between North Korea and the US as Pyongyang seeks to expand its nuclear weapons program.

Rodman has visited North Korea at least four times to engage in what he terms "basketball diplomacy".

During a visit in 2014, the five-time NBA champion sang Happy Birthday to Kim Jong Un at a Pyongyang stadium and then walked forward and bowed to the hardline leader.

The tribute by Rodman, 56, to a man he has called a "friend for life," triggered outrage in the US.

"I think he's an idiot," US Senator John McCain said at the time.

Rodman also endorsed US President Donald Trump during his campaign for the top job, saying he had been "a great friend for many years" in a 2015 tweet.

- DPA, AAP