Earlier on Thursday, University of Cincinnati Medical Center spokeswoman Kelly Martin told reporters that "Otto is in stable condition but he has suffered a severe neurological injury".
On Thursday, the State Department said that U.S. diplomat Joseph Yun, who negotiated Mr Warmbier's release, had also met with three other USA citizens being held in North Korea.
He described his son's return as bittersweet. While driving away, he saw a group of about 150 people wearing blue and white shirts, and ribbons of the same color combination, in support of Otto at a nearby intersection.
The student was sentenced in March last year to 15 years of hard labour.
Otto Warmbier's father, Fred, said today that he does not believe North Korea's claim that his son's coma resulted from "botulism and a sleeping pill".
"I call on them to release the other Americans being held", he urged about three other United States citizens still being detained by the rogue regime.
"We did what we could, we tried to stay low, we were advised that it was important that you don't upset the North Koreans", Warmbier said.
The State Department is continuing to discuss three other detained Americans with North Korea.
North Korea said Thursday it released Warmbier over "humanitarian" reasons, its first official comment since he was returned to his home state of OH in a coma.
Doctors said after conducting several tests, they haven't found anything that suggests he had contracted botulism.
Fred Warmbier said of his son's release: "They did not do this out of the kindness of their hearts". Asked if the administration of former President Barack Obama had done enough to secure their son's release, Warmbier said: "The results speak for themselves". "Otto, I love you so much, I'm insane about you and I'm so glad you're home".
Warmbier's full interview will air Thursday night on Fox News. But it emerged as he traveled back home that Warmbier, a University of Virginia student, was in a coma.
The video, which TIME obtained from Cincinnati station WCPO, show Warmbier being placed in an ambulance, after which he was transported to a local hospital to receive treatment. Joy at his release was mixed with concern over his condition. He said his son will now get medical care that he was denied in North Korea.
Warmbier's doctors held a press conference on Thursday that starkly contrasted North Korea's explanation of his condition. He called North Korea a "pariah" and "terrorist" state.
Such detentions in the totalitarian nation have added to tensions between Washington and Pyongyang.
North Korea has broken its silence on the release of American detainee Otto Warmbier.