Hillary Clinton on Wednesday looked to head off further questions about her health, releasing new medical records showing she is "fit to serve" as president and recovering from "mild" pneumonia as she prepares to resume her campaign.

The disclosure came as her Republican rival Donald Trump -- in a media-savvy move -- released new health data of his own during the taping of a nationally televised medical chat show set to air Thursday.

Both candidates, among the oldest ever to run for the White House, were under intense pressure to share more medical information after Clinton fell ill during a 9/11 ceremony in New York on Sunday and was forced to leave.

Recent opinion polls have shown the gap between the two candidates narrowing, with less than two months to go before Election Day, and the presidential hopefuls disclosed fresh information in a bid to score points with undecided voters.

In a detailed, two-page "summary update" on Clinton's health, her personal physician Lisa Bardack wrote that the 68-year-old was bouncing back after a diagnosis of "mild, non-contagious" pneumonia.

She "is recovering well with antibiotics and rest" after being laid low over the weekend, when she suffered from fatigue and a low-grade fever, although her vital signs remained normal, Bardack said.

The Democratic White House nominee "continues to remain healthy and fit to serve as president of the United States," she wrote, noting she is in "excellent mental condition."

After Clinton was seen stumbling limp-legged into her vehicle Sunday at Ground Zero, it took several hours for her personal physician to disclose she had been diagnosed with pneumonia two days earlier, drawing criticism of her campaign's transparency.

Clinton was at home in Chappaqua, New York for a third straight day Wednesday, recovering from a health scare that has rocked her bid to become America's first woman president.

News of Trump's appearance on "The Dr. Oz Show" -- though it appeared to reveal little detail -- had earlier flooded the US airwaves on Wednesday, upping the pressure on Clinton to share more health data before returning to the trail Thursday with appearances in North Carolina and Washington.

- 'I have it right here' -
So far the 70-year-old Trump had released only four, gushing paragraphs on his health, written by his doctor Harold Bornstein in December 2015.

Following the revelation of Clinton's pneumonia, Trump vowed soon to release "very, very specific numbers" from a recent check-up with Bornstein.

Team Trump had raised -- then dropped -- the possibility of releasing them during an appearance on "Dr. Oz".

But during recording of the segment Wednesday morning, Trump finally did present its celebrity host with the results, according to a statement on the show's website.

In a snippet teased on the site, Mehmet Oz -- who is also a professor of surgery at Columbia University in New York -- is seen asking Trump:

"If your health is as strong as it seems... why not show your medical records?

"Well, I have really no problem in doing it," Trump responds. "I have it right here. Should I do it? I don't care."

The Republican nominee goes on to pull the documents from his pocket, to cheers and applause from the show audience.

- 'Slightly overweight' -
A statement from the medical chat show said their hour-long one-one-one interview touched on Trump's cardiovascular health, family medical history and history of cancer, among other topics.

But the actual details revealed appeared to remain very generic.

According to US media who attended the taping, Oz declared Mr. Trump "slightly overweight" at 267 pounds (120 kilos) for roughly six foot two inches (1.88 meters).

Audience member Kelly Platt -- a pharmacist intern and Trump supporter -- told CNN that Oz deemed Trump's cholesterol to have come down to a safe level, thanks to medication.

Clinton campaign manager Robby Mook ridiculed Trump's TV appearance.

"His Doctor Oz charade is as completely unserious as his original joke of a letter written in five minutes," Mook said. "He continues to hide his taxes and business dealing behind fake excuses. And it begs the question: what is he trying to hide?"

- On the trail -
Trump continued his barnstorming of key battleground states Wednesday with stops in Michigan and Ohio. On Thursday, he is due to deliver a major economic speech.

During a stop in Flint, Michigan on Wednesday, Trump was interrupted by the Methodist pastor at a church he was visiting when he launched into a critique of Clinton's foreign policy.

"Mr Trump, I invited you here to thank us for what we've done in Flint, not give a political speech," said the pastor, Faith Green Timmons.