Democratic presidential candidate Kamala Harris holds a narrow lead over Republican rival Donald Trump in six US swing states and is tied in a seventh, according to a Bloomberg poll of likely voters released on Friday.

Her leads in individual states are within the poll's statistical margin of error, underscoring that the Nov. 5 contest could be decided by the narrowest of margins, it said.

The Bloomberg News/Morning Consult poll shows Harris leading by seven percentage points in Nevada, five points in Pennsylvania, three points in Arizona, Michigan and Wisconsin, and two points in North Carolina. The two are tied in Georgia.

Across the seven states, Harris is ahead by three percentage points among likely voters, a lead that is two points higher than last month.

In a sign of her recent momentum, some 47% of likely voters think she will win the election, regardless of whether they back her, compared with the roughly 40% who said Trump would win.

A new Reuters/Ipsos poll earlier this month showed Trump's campaign vow to increase tariffs on imported goods has the support of a narrow majority of voters, illustrating his economic advantage over Harris.

A New York Times poll of battleground states released on Monday showed Trump was narrowly ahead in Arizona, Georgia and North Carolina.

The Bloomberg poll said Trump still maintained an advantage over Harris on who would be better at handling the economy, but his lead is narrowing. His advantage was just 4 percentage points in the latest poll, down from 6 points in August.

On the question of immigration, Trump enjoys a 14-point trust advantage among likely voters, even though during a Sept. 10 debate he amplified a false claim that Haitian immigrants in Springfield, Ohio, were eating residents' pets.

The poll surveyed 6,165 registered voters in seven swing states and was conducted online from Sept. 19 to Sept. 25. Likely voters totaled 5,692. For both registered and likely voters, the statistical margin of error is plus or minus 1 percentage point across the seven states.

For the individual states, the margin of error was 3 percentage points in Arizona, Georgia, Michigan, North Carolina, Pennsylvania and Wisconsin, and 4 points in Nevada.