Democratic President Barack Obama has defeated Republican nominee Mitt Romney in Pennsylvania and won the state's 20 electoral votes.

His win extends the state's streak of supporting Democrats to six elections.

No Democrat has won the White House without Pennsylvania in 64 years.

Obama's victory in Pennsylvania was his second straight, he beat Republican John McCain in 2008 by 10 percentage points.

Reacting to the news in Philadelphia, Mayor Michael Nutter said, "It's an incredible night, a historic night. I could not be happier. The president deserved to be re-elected."

Nutter then said that Philadelphia, and Pennsylvania, could have played an integral role in Obama's defeat of Republican Mitt Romney. A key to the race going in was driving turnout, and Nutter said it was driven to higher levels than four years earlier.

"It looks like we gave Obama a larger margin of victory out of Philadelphia than in 2008. If we did, that'd be incredible," Nutter said via cell phone from a Center City victory party.

With 96.98 percent of the vote counted, Obama got 551,070 votes to Romney's 90,989. The margin of victory: 460,081 votes.

In a concession speech delivered in Boston, Republican hopeful Mitt Romney said his team had "left everything on the field," telling supporters the "election is over." He said he would pray for Obama in his second term.