An American student who fell into a coma while imprisoned in a North Korean labor camp returned to the United States late Tuesday after Pyongyang allowed him to be flown home, US media reported.

A military aeroplane carrying Otto Warmbier landed in his hometown of Cincinnati shortly before 10:20pm (0220 GMT Wednesday), CBS News reported.

The release of Warmbier, 18 months into a 15-year sentence, came as US President Donald Trump invited South Korea's new leader Moon Jae-In to Washington for talks on the escalating stand-off over the North's nuclear program.

Secretary of State Rex Tillerson said earlier in the day that his agency had "secured" 22-year-old Warmbier's release during discussions with North Korea, and is pushing for three more Americans to be freed. It was not immediately clear if he had made any concessions.