Republican Donald Trump has swept to victory in five northeastern state primaries, while Democrat Hillary Clinton is projected to win Maryland and Delaware.
The projections based on exit polls showed commanding leads for the candidates as broadcasters called the races shortly after polls closed at 8pm local time on Tuesday in all five states where voting took place.
The front-runners hoped to cement their leads by amassing substantial portions of the delegates up for grabs in Maryland, Pennsylvania, Delaware, Connecticut and Rhode Island.
Results remained outstanding in three of the Democratic contests.
Trump's win in Pennsylvania came in the largest state up for grabs on Tuesday, but complicated delegate allocation rules mean that only a small portion of the state's 71 delegates will go outright to the winner of the state vote.
Republican challengers Ted Cruz and John Kasich have been trying to co-ordinate in upcoming contests to prevent Trump from securing the 1237 delegates needed to win the nomination outright at the party convention in July.
Among Democrats, Clinton held strong double digit poll leads over rival Bernie Sanders in Pennsylvania and Maryland ahead of the vote, but had a narrower lead in Connecticut. Clinton claims roots in Pennsylvania, where her father grew up.
She plans to hold an election night rally on Tuesday in Philadelphia, the same city where the party convention is scheduled to be in July.
Sanders meanwhile was looking forward to states yet to vote with a rally on Tuesday evening in West Virginia.
He pointed to his campaign's success coming from relative obscurity to seriously challenge the Clinton juggernaut.
