Dennis Rodman singing "Happy Birthday" to North Korean regime chief Kim Jong-Un was akin to Marilyn Monroe performing for JFK, tourists who watched the performance said Thursday.

Hollywood sex symbol Monroe serenaded John F. Kennedy with a sultry version of the song at a Democratic Party fundraising soir�e in 1962.

Rodman, formerly of the Chicago Bulls, sang the tune to Kim on Wednesday before joining fellow players for a game marking the reclusive leader's birthday, which has sparked huge controversy in the US.

"It was a little Marilyn Monroe to JFK, the tone of it," American Sophia Sokmensuer, who was in the audience in Pyongyang, told reporters Thursday at Beijing airport.

Rodman gestured to the crowd and appeared to bow to Kim, as a team of blue-clad retired NBA team-mates and North Korean players clapped along.

"Everyone was clapping and it was nice and it was funny," the New York University education student added.

She said the game "was fascinating to see and a lot of fun".

"At first it was a little tense but it relaxed and it was nice," she added.

Sean Agnew, a club owner from Philadelphia, described Rodman's song as "weird".

"He just sort of did it off the cuff, and it was, you know, obviously awkward," Agnew told AFP.

Rodman's teammate and former NBA player Eric 'Sleepy' Floyd was among the passengers arriving in Beijing.

He ran past reporters with his jacket over his head, refusing to answer questions as he was ushered away in a black car.

It is unclear when Rodman or the other players will return from North Korea.

The heavily tattooed former All-star arrived in Pyongyang on Monday for his fourth trip to the North in 12 months, together with an assembled team of other former NBA players including Doug Christie, Craig Hodges and Charles Smith, for the exhibition game.

Rodman has been widely criticised for failing to raise human rights issues or the plight of jailed American Kenneth Bae during his visits to the North and with Kim, whom he calls his friend for life.