The second summit between North Korean leader Kim Jong Un and President Trump is underway as the two leaders shook hands in Hanoi on Wednesday.
Trump says he was not walking back on U.S. demands for North Korea's denuclearization.
Kim said they had overcome obstacles to hold the summit in Vietnam and had needed patience since their first meeting in Singapore last year. He said he hoped these talks would be successful, according to Reuters.
Trump and Kim are scheduled to hold a 20-minute discussion followed by a dinner with aides.
Joining Trump will be Secretary of State Mike Pompeo and acting Chief of Staff Mick Mulvaney.
Kim will be joined by his top envoy, Kim Yong Chol, and Foreign Minister Ri Yong Ho.
The White House said the two leaders will hold "a series of back and forth" meetings on Thursday.
Trump tweeted: "Vietnam is thriving like few places on earth. North Korea would be the same, and very quickly, if it would denuclearize," Trump said on Twitter ahead of his meeting with Kim.
"The potential is AWESOME, a great opportunity, like almost none other in history, for my friend Kim Jong Un. We will know fairly soon - Very Interesting!"
In Singapore at the first summit between the two last June, Trump and Kim pledged to work toward denuclearization and permanent peace on the Korean peninsula.
North and South Korea have been technically at war since their 1950-53 conflict, with the Americans backing the South, ended in a truce, not a treaty.