U.S. Vice President Kamala Harris leads Republican rival Donald Trump by 5 percentage points in an NBC News poll released on Sunday that found that respondents have come to see her more favourably since she emerged as the Democratic candidate for president.

Asked about their views of Harris since she became the nominee, 48% of 1,000 registered voters surveyed said it was positive compared to 32% in July — the largest jump among politician ratings polled by NBC since President George W. Bush's favorability rose after the Sept. 11, 2001, attacks.

Asked about Trump, 40% of those polled said they viewed him positively compared to 38% in July, the news network said. The poll, conducted Sept. 13-17, has a margin of error of 3 percentage points.

A separate CBS News poll also found Harris leading Trump, by 4 percentage points, 52% to 48%, among likely voters, with a margin of error rate of plus or minus 2 percentage points.

The findings are broadly in line with other recent national polls, including those by Reuters/Ipsos, that show a close contest heading into the Nov. 5 election.

While national surveys offer important signals on the views of the electorate, the state-by-state results of the Electoral College determine the winner, with a handful of battleground states likely to be decisive.

Trump, 78, is making his third consecutive bid for the White House after losing to Joe Biden in 2020, which he continues to falsely blame on widespread voter fraud while facing federal and state criminal charges over efforts to overturn the election results.

Harris, 59, is a former U.S. senator and prosecutor now serving under Biden. She would be the first woman to serve as president in the nation's 248-year history.

"She's been able to change this from a race that was a referendum on Joe Biden to a race that is a referendum on Donald Trump," Amy Walter, publisher and editor in chief of the nonpartisan Cook Political Report, told NBC's "Meet the Press."

In CBS' poll of 3,129 registered voters surveyed Sept. 18-20, Harris edged up 2 percentage points after a 50-50 split in August, shored by her performance in the Sept. 10 debate and brightening economic news.