Three US citizens are on their way home after being released from a North Korean prison less than an hour before secretary of state Mike Pompeo’s official plane was about to take off.

US President Donald Trump announced the three men’s release late Wednesday night, calling it a “positive gesture of goodwill” on the part of North Korea.

The plane carrying the party arrived in Alaska for refuelling and there’ll be a reception upon arrival in Washington.

Mr Trump said he would greet Mr Pompeo and the former detainees when they landed at Andrews Air Force Base outside Washington at 2am Thursday morning local time.

“I am pleased to inform you that Secretary of State Mike Pompeo is in the air and on his way back from North Korea with the 3 wonderful gentlemen that everyone is looking so forward to meeting. They seem to be in good health,” the President wrote in a post on Twitter.

Secretary Pompeo and his “guests” will be landing at Andrews Air Force Base at 2:00 A.M. in the morning. I will be there to greet them. Very exciting!

— Donald J. Trump (@realDonaldTrump) May 9, 2018

The Associated Press reported North Korea’s release of the three men played out amid “high-stakes diplomacy” and was only sealed about an hour before Mr Pompeo took off from Pyongyang.

After meeting North Korean leader Kim Jong-un, Mr Pompeo had given a fingers-crossed sign when asked if there was good news, the AP reported.

A North Korean emissary came to the hotel shortly after to say the detainees were being freed.

“The three men finally left custody at 7:45 pm local time, and by 8:42 pm they were flying home,” it said.

South Korea heralded the release as positive for upcoming talks between Mr Trump and Kim, and called on Pyongyang to also release six South Korean detainees.

Mr Pompeo travelled to North Korea to pave the way for Mr Trump’s summit. Photo: AP

Mr Trump said details of the meeting with Kim would be released within days, but it would not be held at the demilitarised zone between the two Koreas.

Mr Pompeo arrived in the North Korean capital Pyongyang on Wednesday morning from Japan and headed to the Koryo Hotel for meetings.

The three US detainees released are Korean-American missionary Kim Dong-chul, Kim Sang-duk – also known as Tony Kim — and Kim Hak-song.

Mr Dong Chul was arrested in October 2015 when he allegedly to meet with a former North Korean soldier to receive classified information.

Mr Hak Song and Mr Kim were detained in 2017 and charged with “hostile acts” against the North Korean state.

“We are very grateful for the release of our husband and father, Tony Kim, and the other two American detainees,” the Kim family said in a statement.

I had productive meetings in Pyongyang with Chairman Kim Jong-un and made progress. I'm delighted to bring home three Americans.

— Secretary Pompeo (@SecPompeo) May 9, 2018

Until now, the only American released by North Korea during Mr Trump’s presidency was Otto Warmbier, a 22-year-old university student who returned to the United States in a coma last summer after 17 months of captivity. He died days later.

Mr Warmbier’s death escalated tensions already running high at the time over Pyongyang’s stepped-up missile tests.

The upcoming summit has sparked a flurry of diplomacy, with Japan, South Korea and China holding a high-level meeting in Tokyo on Wednesday.

However, North Korea reminded the United States on Wednesday there still was tension between them, warning it against “making words and acts that may destroy the hard-won atmosphere of dialogue,” the North’s state media said.

-with agencies