He previously met the leader Kim Jong-un while watching an exhibition match between U.S. players and North Korean players at Pyongyang's Indoor Stadium What is he doing in North Korea?
He told reporters before departing Beijing airport on Tuesday that he is "just trying to open a door" with North Korea.
Rodman, one of the few people to know both Trump and Un, sported a black T-shirt advertising a marijuana cybercurrency as he talked to reporters briefly before his flight from Beijing to the North Korean capital.
He's likely to face similar accusations now: His visit comes amid global condemnation over North Korea's accelerating efforts to develop nuclear weapons and missiles, which poses one of the toughest foreign policy challenges for President Donald Trump.
Rodman's trip to North Korea is at least his fifth time to the reclusive nation.
In April, Trump called Kim a "pretty smart cookie" and in May, he said he would be "honored" to meet the North Korean leader "under right circumstances".
Warmbier was on a New Year's Eve tour in North Korea, en route to Hong Kong, where he was to do a January study-abroad trip.
Warmbier's parents told The Washington Post on Tuesday that their son has been in a coma for more than a year since his last public appearance at a North Korean trial in March of 2016. A spokesperson for the Richardson Foundation, which has been working with the Warmbier family to secure Otto's release, confirmed the report to Vice News and said Otto's condition is critical.
The State Department is continuing to discuss the situation of three other detained Americans with North Korea, Tillerson said. He arrived in North Korea on Tuesday. Rodman has previously appeared on the Trump-hosted reality show The Apprentice, and endorsed Trump during the 2016 presidential campaign.
The US State Department stressed Rodman is not going to North Korea in any official capacity, and the National Basketball Association hall of famer has refused to give further details.
Tillerson told USA senators at the start of a budget hearing that the State Department had no comment on Mr Warmbier's condition, "out of respect for him and his family".
"Our son is coming home", Fred Warmbier told The Post on Tuesday morning after Otto Warmbier was evacuated.
"Apparently our message is not being conveyed properly due to the circumstances that are much bigger than us", Smith told The Associated Press before the exhibition game.
Former Detroit Pistons and Chicago Bulls star Dennis Rodman is reportedly on his way back to North Korea. At the same time, his trips have also faced ridicule and criticism from some US politicians and activists who view them as fodder for North Korean propaganda.
Rodman routinely distances himself from political events in North Korea.
Tillerson said the State Department is still working to secure the release of three other US citizens detained in North Korea.
Pyongyang has unleashed a string of missile launches and tests of other advanced weaponry in recent weeks as it seeks to highlight its progress toward mastering the technology needed to mount a nuclear warhead on an intercontinental ballistic missile. Instead, he was sentenced to 15 years of hard labor.
Before his trial, Mr Warmbier said he tried to steal the propaganda sign as a trophy for an acquaintance who wanted to hang it in her church.
Rodman is heading to North Korea later Tuesday from Beijing.
While in North Korea, the 22-year-old contracted botulism and is in "bad shape" but is now en route back to the United States, a source close to the family revealed to CNN.