Republican presidential candidate Donald Trump speaks at the Grand Park Events Center on July 12, 2016 in Westfield, Indiana, US. Trump is campaigning amid speculation he may select Indiana Gov. Mike Pence as his running mate. [Photo/VCG]

WASHINGTON - Republican Donald Trump conducted last-minute talks with his top potential picks for his vice presidential running mate on Wednesday and said he would announce his choice on Friday in New York.

"I will be making the announcement of my Vice Presidential pick on Friday at 11am in Manhattan. Details to follow," the presumptive Republican presidential nominee tweeted on Wednesday night.

Trump had a breakfast meeting on Wednesday with Indiana Governor Mike Pence, and later sat down for talks with former US House of Representatives Speaker Newt Gingrich. His family met on Tuesday with New Jersey Governor Chris Christie, who speaks to Trump on a near-daily basis.

In addition, US Senator Jeff Sessions, 69, of Alabama, a fourth potential candidate for the No 2 spot who has been a close adviser to Trump, was seen going into the Conrad Hotel in Indianapolis, where Trump was.

A source close to the campaign said Trump appeared to be leaning toward Pence but that he could always change his mind. "It's not done until it's done," the source said.

Trump seemed to be trying to decide between Pence and Gingrich, the source added.

The New York businessman is to be formally nominated at the Republican National Convention next week in Cleveland. Traditionally, the vice presidential choice is used to build enthusiasm among party loyalists.