The President made the comment as the total number of American’s killed by coronavirus nears 200,000. Kim Jong-un maintains power in North Korea via a brutal system of concentration camps, where torture is reported to be widespread, and has ordered the execution of a number of political rivals.
Mr Trump has previously been criticised for his relationship with Kim Jong-un after claiming “we fell in love” at a 2018 rally.
Taking to Twitter the president commented: “Kim Jong-un is in good health. Never underestimate him!”
There have been persistent rumours the North Korean dictator is suffering poor health over the last few months.
South Korean analyst Chang Song-min, who advised one of the country’s former presidents, claimed his sister Kim Yo-jong was being groomed in case a successor is needed.
However, North Korean state media last month released photographs purported to show Kim Jong-un attending a meeting of the politburo, the country’s governing body.
After Mr Trump made his comments a number of Democratic congressmen harshly criticised them on Twitter.
Don Beyer, who represents Virginia’s eight congressional district, said: “Trump is more concerned about Kim Jong un’s health than he is about the health of American students and educators.
“He keeps insisting schools must reopen immediately, but isn’t doing a thing to keep them safe.”
Mr Trump’s comments were also condemned by a number of US reporters.
CNN’s Jake Trapper said: “Was anyone remotely concerned about the health of a North Korean dictator in the midst of a pandemic that has killed more than 191,000 Americans?”
In addition, Kathryn Watson, a White House reporter for CBS News, added: “Americans were really worried about the health of a dictator who executes and starves his own people.”
Mr Trump is the first American president to have met a North Korean leader in person.
In 2018 he held a summit with Kim Jong-un in Singapore, followed up by a second the next year in Vietnam.
The two leaders also met in 2019 along the North-South Korean border.
The United States has been pushing unsuccessfully for North Korea to give up its nuclear weapons programme.
During a 2018 rally Mr Trump described his negotiations with Kim Jong-un to supporters.
He said: “Americans were really worried about the health of a dictator who executes and starves his own people.
“And then we fell in love, okay? No, really – he wrote me beautiful letters, they’re great letters.”