Republican Donald Trump pulled even with Democratic rival Hillary Clinton in a Reuters/Ipsos opinion poll released on Wednesday, in a dramatic early sign that the Nov. 8 presidential election might be more hotly contested than first thought.

After weeks of trailing Clinton in head-to-head polls, the billionaire businessman's numbers jumped after he effectively won the Republican nomination last week when his two remaining rivals quit, according to the online survey.

The national poll found 41 percent of likely voters supporting Clinton and 40 percent backing Trump, with 19 percent undecided. The survey of 1,289 people was conducted over five days and has a credibility interval of 3 percentage points.