(VOVworld) - Democrat candidate Hillary Clinton is leading Republican Donald Trump in key states in the race for the White House, according to opinion polls earlier this week.

Clinton addresses the public in Kissimme, Florida. (Photo: EPA/VNA)

NBC News/Wall Street Journal/Marist polls revealed that in Pennsylvania, Clinton has extended her lead over Trump by 11 points. Lee Miringoff, Director of the Marist College Institute for Public Opinion, said the results should be an alert to Trump because the three states - Pennsylvania, Iowa, and Ohio - are key elements in his formula for success. Voters in these three states has usually supported the Republican nominee in previous elections.

According to an independent Quinnipiac University poll, Clinton is ahead of Trump in Pennsylvania and Ohio while the two have equal support in Florida, a critical state in the South.