The White House said there was nothing unusual about President Donald Trump making a surprise trip to the Walter Reed Medical Center on Saturday to undergo what he called "phase one" of his annual physical.

But the hospital visit was met with skepticism online, where some felt the White House and the president weren't being upfront about it.

"Visited a great family of a young man under major surgery at the amazing Walter Reed Medical Center," Trump tweeted early Sunday morning. "Those are truly some of the best doctors anywhere in the world. Also began phase one of my yearly physical. Everything very good (great!). Will complete next year."

Trump, 73, had no public events on his calendar Saturday and no advance guidance was given that he would be getting any kind of medical exam. Trump's prior two physical exams as president were on the public schedule and advance warning was provided. In addition, those exams did not take place in multiple "phases." Trump's most recent physical was in February.

Trump arrived at the hospital at 2:45 p.m. Saturday and spent slightly more than two hours there. He was seen leaving with a tan envelope tucked in his arm. The full annual presidential physical typically takes several hours and is unlikely to be described as a "quick exam and labs," which is how White House press secretary Stephanie Grisham explained the visit afterward.

"Unless the healthiest man alive is shifting to fiscal year reporting, two medicals in the same year ain’t annual, it’s biannual," tweeted Philippe Reines, who was a top aide to 2016 Democratic presidential nominee Hillary Clinton, whose health was also scrutinized during her campaign.

"Perfect example of how the long history of false statements from White House has worn away any presumption of truthfulness," David Lauter, the Los Angeles Times' Washington bureau chief, tweeted. "Maybe Trump's hospital visit was routine, but burden of proof is on WH to show evidence."

As Trump was at the hospital, Grisham said, "Anticipating a very busy 2020, the president is taking advantage of a free weekend here in Washington, D.C., to begin portions of his routine annual physical exam at Walter Reed." Afterward, she said Trump "remains healthy and energetic without complaints, as demonstrated by his repeated vigorous rally performances in front of thousands of Americans several times a week."

Later in the evening, Grisham told NBC News in a statement that Trump "is fine — perfectly healthy."

"It was a routine checkup," she said. "Speculation of this nature is irresponsible and dangerous for this country."

Speaking with Fox News host Jeanine Pirro on her Saturday program, Grisham said Trump is as "healthy as can be" and that he's "got more energy than anybody in the White House."

"You know, Stephanie, he's almost superhuman," Pirro responded. "I don't know how anyone can deal with what he's dealing with. I get frustrated with what's going on in Washington. I want to throw things at the television. But I don't."