Washington, Aug 22 (IANS): Frontrunner Republican presidential hopeful Donald Trump moved his campaign into high gear, reiterating his pledge to build a wall to prevent illegal immigrants and saying Congress could end the guarantee of citizenship for their US-born children.

"The 14th Amendment - I was right on it. You can do something with it, and you can do something fast," Trump told thousands of people gathered to hear the real estate mogul speak at a huge rally in a stadium in Alabama Friday.

"In the case of other countries, including Mexico, they don't do that. It doesn't work that way. ... We're the only place just about that's stupid enough to do it," he said at the rally in the midst of several key Southern states.

Ratified on July 9, 1868, the 14th Amendment to the US Constitution granted citizenship to "all persons born or naturalised in the United States," which included former slaves recently freed.

"We're going to build a wall," Trump told his enthusiastic supporters who filled about half of the 43,000-seat Ladd-Peebles Stadium in Mobile, according to media reports.

Trump's campaign had moved Friday's "pep rally" from the city's Civic Centre, which seats about 4,000, to the stadium in anticipation of the huge crowd.

He extolled his own skills as a businessman as he took a swipe at establishment favourite Jeb Bush and asked: "Who would you rather have negotiate with China, Japan, Mexico, any other: Trump or Bush?"

The crowd cheered, and some began to chant "Trump! Trump! Trump!"

Trump has been drawing large crowds during stops in key primary states like New Hampshire with his attacks on traditional politicians accusing them of being controlled by lobbyists.

"All these guys like Bush and Hillary (Clinton), they're taken care of," he said.

"The reason I have this really incredible enthusiasm, the reason I have it is because I know what I'm doing," Trump said.

"And I don't say that in a bragging way. You people are looking for somebody who knows what he's doing."

He also criticized the Iran nuclear deal, saying that Secretary of State John Kerry's bicycle accident during the Iran negotiations in which he broke his leg "was the good part of the deal."

Like other Republican candidates, Trump said he would repeal President Barack Obama's signature healthcare law, but did not say what he would replace Obamacare with.

"We're gonna fix it. Healthcare we're gonna fix it. Women's health issues. We're gonna fix it," he said.

Trump promised that as president his "whole energy, my whole being is going to make our country rich and make our country great again."

Trump also addressed another top issue - his wacky hairstyle. On a hot and humid night, Trump looked upwards and joked: "If it rains I'll take off my hat and prove, I'll prove, once and for all, that its mine," while stroking his hair.