Presumptive Republican presidential nominee Donald Trump has formally introduced Mike Pence as his vice presidential running mate in a joint conference, describing the Indiana governor as a job creator and budget balancer who will help unify the party.

Key points: Trump delivered a rambling speech slamming Clinton, Islamic terrorism

Trump delivered a rambling speech slamming Clinton, Islamic terrorism Pence delivered a prepared introductory speech promoting Trump

Pence delivered a prepared introductory speech promoting Trump Trump confirms the reason for Pence pick is 'Republican party unity'

In a bid to broaden his appeal to a fractured Republican electorate, Mr Trump presented Mr Pence as a perfect complement for the White House: a veteran of government who can guide an outsider, a man with a Midwestern sensibility and strong Republican credentials.

"Indiana governor Mike Pence was my first choice, I've admired the work he's done, especially in the state of Indiana," Mr Trump said at the press event in New York City.

In a rambling 29-minute speech that often deviated from prepared remarks, Mr Trump spoke at length about Democratic rival Hillary Clinton, Islamic terrorism, and his own proposals, before finally interrupting himself by saying "back to Mike Pence" and offering his motivation for the selection.

In sharp contrast, Mr Pence delivered a prepared speech that highlighted his own biography and then made a case for electing Mr Trump president.

"Let's come together as a party, as a people, as a movement, to make America great again and that day begins when Donald Trump becomes the 45th president of the United States of America," Mr Pence said.

Mr Trump and Mr Pence made their debut just two days before the beginning of the Republican National Convention in Cleveland, where delegates from around the country will convene to officially nominate the pair as their party's ticket for the November 8 election.

Mr Trump's decision to select Mr Pence was seen as a move to unify the Republican Party, which remains deeply divided in the wake of the New York real estate mogul's primary victory.

Mr Trump has struggled to bridge the gap between himself, a self-described outsider, and the establishment and conservative wings of the party.

'Outsider' Trump seeks to unite Republican party

The selection of Mr Pence was widely praised by conservatives within the Republican party, many of whom continue to argue that Mr Trump lacks conservative credentials, making them weary about supporting him.

Mr Trump acknowledged that the choice was about unifying the party.

"And one of the reasons is party unity, so many people have said, party unity. Because I'm an outsider," Mr Trump said.

The two appeared on stage together only momentarily at the Hilton Hotel in Manhattan, each addressing the media and about 100 supporters who assembled for the event without the use of a teleprompter.

Mr Trump spoke first, while Mr Pence stood off stage out of view — he then exited the stage while Mr Pence spoke, and the two shook hands afterward and posed for pictures with supporters.

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Mr Trump, 70, chose Mr Pence, 57, over two politicians he considers friends and close advisers, former House of Representatives speaker Newt Gingrich, 73, and New Jersey governor Chris Christie, 53.

Democratic rival Mrs Clinton has been quick to criticise Mr Trump's vice presidential pick as "Donald Trump with a different haircut" while slamming his policies on Twitter.

Some of those policies include Mr Pence's pro-life stances on abortion and the slashing of education funding.

Meanwhile, Mr Trump described meeting with Mr Pence's family, including his wife and daughter, as part of the motivation for selecting him as a running mate.

"He looks very good," Mr Trump said, discussing Mr Pence's appearance.

Mr Trump also jabbed lightly at Mr Pence for not endorsing him during the Indiana Republican primary contest.

Mr Pence delivered a statement at the time that praised both Mr Trump and rival Ted Cruz, the US senator from Texas.

"It was the single greatest non-endorsement I've ever had," Mr Trump said.

AFP/Reuters