Hillary Clinton has expanded her lead over Donald Trump nationally, according to an NBC News/SurveyMonkey Weekly Election Tracking Poll released Tuesday.

Among likely voters, the poll found 50 percent support Clinton and 45 percent back Trump. Among registered voters, Clinton leads by 6 percentage points -- 49 percent to 43 percent.

With third-party candidates involved, Clinton leads Trump by 5 percentage points -- 45 percent to 40 percent. Ten percent said they back Libertarian Gary Johnson and 4 percent said they support Green Party candidate Jill Stein.

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The poll found 56 percent of likely voters think Clinton will win the presidency and 39 percent said the same about Trump.

Last week, the tracking poll found Clinton led Trump by only 4 percentage points nationally.

The latest poll surveyed 13,326 adults between Sept. 12 and 18 with a 1.2 percentage point margin of error.