North Korea has released Otto Warmbier, a US university student who has been held captive there since January 2016, US Secretary of State Rex Tillerson said today.

Warmbier, a University of Virginia student from suburban Cincinnati, is on his way back to the United States, Tillerson said in a statement.

The State Department is continuing to discuss the situation of three other detained Americans with North Korea, Tillerson said.

The Washington Post cited Warmbier's parents as saying he had been medically evacuated from North Korea in a coma.

“Our son is coming home,” Fred Warmbier told the Washington Post on Tuesday.

“At the moment, we’re just treating this like he’s been in an accident. We get to see our son Otto tonight.”

Otto Frederick Warmbier in Pyongyang in March 2016. Photo: Reuters

Tillerson, at a Senate hearing on Tuesday, declined to comment on Warmbier's condition.

His release comes as former US basketball star Dennis Rodman visited the reclusive country. A senior administration official said the Trump administration did not authorise this trip.

"This is him freelancing," the official told Reuters.