President Barack Obama, picking up support following the Democratic National Convention, widened his narrow lead over Republican US presidential challenger Mitt Romney in a new Reuters/Ipsos poll released on Saturday.

The latest daily tracking poll showed Obama, a Democrat, with a lead of 4 percentage points over Romney. Forty-seven per cent of 1,457 likely voters surveyed online over the previous four days said they would vote for Obama if the November 6 elections were held today, compared with 43 per cent for Romney.

"The bump is actually happening. I know there was some debate whether it would happen... but it's here," said Ipsos pollster Julia Clark, referring to the "bounce" in support that many presidential candidates enjoy after nominating conventions.

Obama had leapfrogged Romney in the daily tracking poll on Friday with a lead of 46 per cent to 44 per cent.

The president's lead comes despite a mixed reaction to his convention speech on Thursday night in Charlotte, North Carolina, and Friday's government data showing that jobs growth slowed sharply last month.

Obama's lead over Romney is comparable to Romney's former lead over the president after the Republican National Convention finished last week, Clark said.

"We don't have another convention now to turn our attention to, so (Obama's bounce) may maintain," Clark said. "How big it'll be and how long it will last remains to be seen."

Obama increased his lead over Romney in certain favourable characteristics. Asked who was more "eloquent," 50 per cent of the 1,720 registered voters questioned in the poll favored Obama, compared to 25 per cent for Romney. Asked about being "smart enough for the job," 46 per cent sided with Obama compared to 37 per cent for Romney.

In fact, Obama led Romney in a dozen such favourable characteristics, such as "represents America" or "has the right values." The only such category in which Romney had an advantage was being "a man of faith," as 44 per cent picked Romney, who is Mormon, compared to 31 per cent for Obama, who is Christian.

The Democratic National Convention itself received a rather muted response in the poll. Of those registered voters who had heard, seen or read at least something about it, 41 per cent rated it as "average" and 29 per cent as "good."

The Republican National Convention that wrapped up August 30 in Tampa, Florida similarly was rated "average" by 38 per cent and "good" by 27 per cent in Saturday's polling results.

The precision of the Reuters/Ipsos online polls is measured using a credibility interval. In this case, the poll has a credibility interval of plus or minus 2.7 percentage points. – Reuters