Republican Donald Trump and Democrat Hillary Clinton rolled up wins in north-eastern states yesterday in a major show of strength and immediately turned their fire on each other in a possible preview of a general election matchup.

Trump easily defeated rivals John Kasich and Ted Cruz in all five states that held contests - Pennsylvania, Maryland, Connecticut, Rhode Island and Delaware - with a margin of victory rivalling that of his home state of New York a week ago. He was on a path to winning the vote in every single county in each state.

Clinton, already in control of the Democratic race, defeated challenger Bernie Sanders in Maryland, Delaware, Pennsylvania and Connecticut. Her only loss of the night was to Sanders in Rhode Island.

The two front-runners used victory rallies to snipe at each other in the kind of back and forth that will take place should they win their party's presidential nominations and face off in the Nov 8 election to succeed Democratic President Barack Obama.

"I think she's a flawed candidate and she's going to be easy to beat," Trump said at a news conference at New York's Trump Tower.

Trump (pix), who is to deliver a foreign policy speech in Washington today, criticised Clinton's record as secretary of state and her vote as a US senator from New York in support of the Iraq war. He said her only advantage was as a woman seeking to become the first female US president.

"Frankly if Hillary Clinton were a man, I don't think she'd get five percent of the vote," he said.

Woman card

Clinton, in a victory speech in Philadelphia, took aim at Trump for accusing her of trying to "play the woman card".

"Well if fighting for women's healthcare and paid family leave and equal pay is playing the woman card, then deal me in," she said to cheers.

For the Republicans, the Northeastern battles set the stage for a big contest next week in Indiana. Trump has a small lead in polls in the state but Cruz appears stronger there. Trump needs a victory to get closer to the 1,237 delegates required to win the nomination.

Clinton's strong showing in the Democratic race added to the pressure on Sanders to get out of the race or ease his criticism of her.

In her victory speech, Clinton gave a nod to Sanders and spoke of the need for party unity.

"Whether you support senator Sanders or you support me, there is much more that unites us than divides us," she said.

Clinton's victories yesterday gave her 2,141 delegates, according to the AP, pushing her closer to the 2,383 needed for the nomination.

- Reuters