Donald Trump is aiming for a sweep of all five Northeastern states holding primaries today, including Pennsylvania.

His rivals, meanwhile, are pinning their hopes of stopping the Republican front-runner on a fragile coordination strategy in the next rounds of voting.

For Democratic leader Hillary Clinton, wins in most of today's contests would leave little doubt that she'll be her party's nominee.

Rival Bernie Sanders' team has sent mixed signals about his standing in the race, with one top adviser suggesting a tough night would push the Vermont senator to reassess his bid and another vowing to fight "all the way to the convention".

In addition to Pennsylvania, Connecticut, Delaware, Maryland and Rhode Island hold primaries today.