Real estate mogul Donald Trump has zoomed ahead in the race for the Republican presidential nomination, getting almost twice the support against his closest rivals, the latest national poll showed.

The Washington Post-ABC News poll said Trump earned the biggest lead recorded by any Republican presidential candidate this year, receiving favour from 24 percent of registered Republicans and Republican-leaning independents.

"That is the highest percentage and biggest lead recorded by any GOP candidate this year in Post-ABC polls and marks a six-fold increase in his support since late May, shortly before he formally joined the race," the Washington Post said.

Wisconsin Gov. Scott Walker, who formally announced his White House bid last week, came in second with 13 percent trailed by former Florida Gov. Jeb Bush with 12 percent.

Trump could have gotten more support had he not made disparaging remarks against Arizona Sen. John McCain, who he said should not be considered a war hero for having been captured during the Vietnam War.

The ABC News said Trump dropped into single-digit territory on July 19 following his comments about McCain, who became a prisoner of war in Vietnam after the warplane he was piloting was shot down. Previous to that, Trump was holding steady at 28 percent in the first three nights of polling held from July 16 to 18.

The reality TV star made the remarks against McCain during his appearance on Saturday at the Family Leadership Summit, a day-long gathering of about 3,000 social conservative activists in Iowa that drew nine other Republican presidential candidates.

McCain demanded that Trump should apologise not to him, but to the families of those who sacrificed their lives in the war, saying the businessman's comments were "offensive to war veterans."

"I think the point here is that there are so many men and women who served and sacrificed—and happened to be held prisoner—and to denigrate in any way that service, I think, is offensive to veterans," McCain said, according to MSNBC.

"The best thing to do is put it behind us and move forward," the former 2008 Republican presidential nominee said.

Former Arkansas Gov. Mike Huckabee and Florida Sen. Marco Rubio completed the Top 5 with 8, and 7 percentage points of support, respectively. Retired neurosurgeon Ben Carson Kentucky Sen. Rand Paul were tied at sixth place with 5 percentage points each.

Texas Sen. Ted Cruz and former Texas Gov. Rick Perry secured the seventh spot with 4 percent support each; New Jersey Gov. Chris Christie at eighth place with 3 percent; former Ohio Gov. John Kasich and Louisiana Gov. Bobby Jindal at ninth place with 2 percent each; former New York Gov. George Pataki and former Pennsylvania Gov. Rick Santorum were at the bottom six with 1 percent each while businesswoman Carly Fiona and New Jersey Gov. Lindsay Graham both received 0 percent support.

Based on an average of most recent national polls, only the Top 10 bets in the early national surveys can qualify for the first Republican debate, which will be held in Cleveland on Aug. 6.