President Barack Obama has widened his lead over Republican US presidential challenger Mitt Romney following the Democratic National Convention, according to a new poll.

The latest daily tracking poll by Reuters/Ipsos showed Mr Obama had a lead of 4 percentage points over Mr Romney.

Of 1457 likely voters surveyed online over four days, 47% said they would vote for Obama if the November 6 elections were held now, compared with 43% 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.

Mr Obama leapfrogged Romney in the daily tracking poll on Friday with a lead of 46% to 44%. 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.

Ms Clark said Mr Obama's lead was comparable to Mr Romney's former lead after the Republican National Convention finished last week.

"We don't have another convention now to turn our attention to, so (Obama's bounce) may maintain," she added.