The 22-year-old, who was imprisoned in North Korea for 17 months, has been in a coma since March 2016 – when he was sentenced to 15 years hard labour by the brutal Kim Jong-un regime.
A senior US official told the New York Times that new intelligence reports said that Mr Warmbier had been repeatedly beaten while in custody.
The official, who was not authorised to publicly discuss intelligence, said there had been earlier fear that the US student had died.
“We learned of this only one week ago. We want the world to know how we and our son have been brutalised and terrorised by the pariah regime in North Korea.”
The University of Virginia student was medically evacuated after a US State Department’s special envoy to North Korea Joseph Yun travelled to Pyongyang and demanded the young man be released on “humanitarian grounds”.
Mr Warmbier was detained in January 2016 and sentenced to 15 years of hard labour in March last year after the reclusive state accused him of trying to steal an item with a propaganda slogan.
According to the witness, Mr Warmbier’s plane landed at 10.15pm on Tuesday local time (3.15 BST on Wednesday) and medical personnel could be seen carrying a male – believed to be the young man.
The person, said to Mr Warmbier, was carried from the plane and did not appear to be moving independently.
A small group of family friends were nearby to celebrate Mr Warmbier’s arrival, cheering and holding signs that read “Pray for Otto” and “Welcome home Otto”, according to the witness.
The man was loaded into an ambulance bound for the University of Cincinnati Medical Centre, where a hospital spokeswoman said he would receive treatment.
Mr Warmbier’s family said they were told by North Korean officials, through contacts with American envoys, that their son fell ill from botulism some time after his March 2016 trial and lapsed into a coma after taking a sleeping pill, the Washington Post reported.
Bill Richardson, a former diplomat who worked on previous negotiations with the hermit state, said: “In no uncertain terms North Korea must explain the causes of his coma.”
US Secretary of State Rex Tillerson said his department is continuing to discuss three other detained Americans with North Korea.