Donald Trump has said the race for the Republican presidential nomination is "over" after romping to victory in five state primaries.
Mr Trump declared himself the Republican's "presumptive nominee" after winning the party's primaries in Pennsylvania, Maryland, Connecticut, Rhode Island and Delaware.
Meanwhile, Hillary Clinton was dominant in four Democratic races, losing just Rhode Island to her rival Bernie Sanders.
Mr Trump's victories have boosted his delegate total as he aims to reach the 1,237 needed to clinch his party's presidential nomination.
Rivals Ted Cruz and John Kasich have formed an alliance to try to stop Mr Trump from reaching the figure before the Republican National Convention in July.
But it failed to prevent Mr Trump's big showing in the north-east, where he won at least 105 of the 118 available delegates.
Speaking at a victory rally in the lobby of Trump Tower in New York, he said: "It's over. As far as I'm concerned it's over."
Despite Mr Trump's solid win in Pennsylvania, the state's primary system means 54 of the delegates elected by voters will be free agents at the Republican convention, able to vote for the candidate of their choice.
Mr Cruz spent Tuesday in Indiana, which votes next week. Indiana is one of Mr Cruz's best chances to slow Mr Trump down. Mr Kasich's campaign has pulled out of the state to boost his chances.
Speaking at a rally in Knightstown, Indiana, Mr Cruz said: "Tonight this campaign moves back to more favourable terrain."
Mr Trump has called his rivals' pact a "faulty deal" and said efforts to push the nomination contest to the convention are evidence of a rigged process that favours insiders.
But Mr Trump continues to divide opinion in his party. In Pennsylvania, exit polls showed nearly four in 10 Republican voters said they would be excited by Mr Trump becoming president, but a quarter said they were scared by the prospect.
Six in 10 Republican voters in Pennsylvania said the campaign has divided the party, whereas seven in 10 Democratic voters in the state said the race between Mrs Clinton and Mr Sanders has energised the Democrats.
With Mrs Clinton's four victories, she now has 88% of the delegates she needs to become the first woman nominated by a major party.
Mrs Clinton urged Mr Sanders's supporters to help her unify the Democratic Party and reached out to Republican voters who may be unhappy with their party's options.
Speaking in Philadelphia, where the Democrats will gather in July for their nominating convention, she said of the Republican candidates: "If you are a Democrat, an independent or a thoughtful Republican, you know that their approach is not going to build an America where we increase opportunity or decrease inequality."
Mr Sanders conceded that he has a "very narrow path" if he wants to become the Democratic nomination adding: "We're going to have to win some big victories."
Mrs Clinton has 2,141 delegates while Mr Sanders has 1,321.
That count includes delegates won in primaries and caucuses, as well as super-delegates - party insiders who can back the candidate of their choice, regardless of how their state votes.
Mr Sanders has vowed to stay in the race until voting ends in June. He is raising millions of dollars and attracting big crowds, including on Tuesday night in West Virginia, where he told his supporters: "You are powerful people if you choose to exercise that power."
While Mrs Clinton's campaign expects Mr Sanders to stay in the race, her advisers are eager for the Vermont senator to tone down his attacks on the former US secretary of state. She has been reminding voters of the 2008 Democratic primary, when she endorsed Barack Obama after a tough campaign and urged her supporters to rally around her former rival.
According to exit polls, less than a fifth of Democratic voters said they would not support Mrs Clinton if she gets the nomination.