Republican presidential nominee Donald Trump has insisted all is well with his campaign even as Republicans grow increasingly worried about a candidate who seems to have gone permanently off-track.

“There is great unity in my campaign, perhaps greater than ever before,” Trump tweeted on Wednesday.

Republican National Committee chairman Reince Priebus is reportedly among a handful of high-profile Republicans considering whether to confront Trump about his approach to his presidential campaign.

But in recent days, as Trump has continued to pursue a feud with the parents of a Muslim American soldier killed in combat in Iraq, pointedly refused to endorse Republican House speaker Paul Ryan and 2008 GOP nominee John McCain in their primary elections and suggested that November’s election would be rigged.

NBC News reported that senior Republicans plan to stage an "intervention" to get the campaign back on message, stressing issues such as jobs and trade deals.

The effort will be led, according to NBC, by Republican National Committee Chairman Reince Priebus and Trump allies former House Speaker Newt Gingrich and former New York Mayor Rudy Giuliani.

"I think some of what Trump has done is very self-destructive," Gingrich told Fox Business Network on Wednesday.

Three prominent Republicans said this week that they would vote for Democrat nominee Hillary Clinton, saying Trump was unfit to serve as president.

But the Trump campaign, on the other hand, aggressively pushed back against reports of bubbling tension within the party as a result of Trump’s behaviour.

“Our campaign just finished our strongest month of fundraising to date, we’re adding talented and experienced staffers on a daily basis and Trump is turning out bigger, more enthusiastic crowds than Hillary Clinton ever could,” spokesman Jason Miller said on Tuesday.