We're in a strong position, says Hillary Clinton

US Democratic Presidential nominee Hillary Clinton on Thursday, who returned to campaign after being diagnosed with pneumonia, said she believes her campaign was performing strongly in the last leg of the 2016 campaign despite polls showing the race tightening nationally and in key swing states.

Speaking to reporters following her first campaign event since she revealed she was diagnosed with pneumonia, the Democratic presidential nominee was asked if she should be doing anything differently now that the race could be close.

"I've always said that it was going to be a tight race. I've said it from the very beginning, whether I was up, down...it didn't matter," Clinton said. "I'm very proud of the campaign that we have put together. I feel like we are in a strong position going into these last weeks," CBS News reported.

What matters now, Clinton said, is who's registered to vote and who turns out to vote on Election Day, November 8.

Nationally, Clinton's lead over Donald Trump has narrowed in recent weeks. A CBS News/New York Times survey released on Thursday found Clinton leads Trump among likely voters by only 2 percentage points, 46 per cent to 44 per cent. In a four-way race involving third-party candidates, they are tied at 42 per cent.

In Iowa, Trump leads Clinton by 8 per cent points in Iowa, 45 per cent to 37 per cent, according to a Monmouth University poll released Thursday.

Before the brief press conference, Clinton spoke to supporters in Greensboro, North Carolina. She had spent the last several days off of the campaign trail, resting at home in Chappaqua, New York. On Sunday, after being helped into a van after leaving the 9/11 memorial event early, her campaign revealed she had been diagnosed with pneumonia two days earlier.

"This was an ailment that many people just power through and that's what I thought I would do as well," Clinton told reporters Thursday. "I didn't want to miss the 9/11 memorial. As a senator at the time, I consider it a sacred moment and I wanted to get there."

She admitted she probably should have taken a pause from the campaign earlier and said, "My campaign has said that they could have been faster" about disseminating information to the public, "I agree with that. I certainly expect them to be focused and as quick as possible."

Asked if she had told her running mate, vice presidential nominee Senator Tim Kaine, D-Virginia, about her diagnosis on Friday, Clinton said, "My senior staff knew and information was provided to a number of people."

Clinton added that she would not get into personal conversations that she's had, but also said she communicated with him and spoke to him again Wednesday night.