Donald Trump steps up insults of rivals on campaign trail

Concord - Republican White House hopeful Donald Trump stepped up attacks on his campaign rivals on Wednesday, insisting none of them have the calibre to become the next president of the United States.

The real estate tycoon was in particularly strident form in New Hampshire, where he officially filed to be on the ballot in the nation's first Republican state primary election.

This small north-eastern state is typically the first to organise its primary elections for the presidential race, scheduled for next February, and candidates court its voters assiduously.

The candidate registering period opened officially on Wednesday and runs until November 20.

But "Mr Trump", as his enthusiastic supporters call him, was determined to demonstrate he is as strong as ever as the latest poll put him neck and neck with retired neurosurgeon Ben Carson.

The Quinnipiac University survey virtually tied Trump and Carson with 24 and 23 percent of the Republican vote respectively, trailed by Florida Senator Marco Rubio at 14 percent and Jeb Bush at four percent.

But for Trump - the softly spoken Carson, who is as calm as Trump is brash, just doesn't have the requisite personality.

"Ben Carson is a super low energy person," he said. Jeb, he added "is a low energy person".

Energy and temperament

"You need tremendous energy and tremendous temperament... to succeed against China... to succeed against India," explained the 69-year-old Trump.

"Ben cannot do the job," he said. "It's got to be somebody with energy and temperament."

He also laid into the ascendancy of 44-year-old Rubio pointing out that his numbers were still far lower than his.

"He is so bad on immigration, when people will find out, there is no way they will vote for him," he said, calling him a "disaster" when it comes to personal finance.

When it came to Bush, he was scathing.

"He goes, 'I'm not a good talker, I don't speak well, I don't debate well, I don't do anything well... but you should vote for me.' That's Jeb Bush. Why would you say these things? This is what's going to negotiate with China?"

Trump on Wednesday retweeted, then quickly deleted, a tweet showing a montage of Bush pictures, including one of him with his former president father and brother next to a Nazi swastika.

Only Ted Cruz, the Texas senator to the right of the party and at 13% in the latest poll, escaped his criticisms, with Trump saying he had good relationship with him.

'Do anything'

Turning to the Democrats, Trump said Hillary Clinton was being protected and scoffed at Vermont Senator Bernie Sanders, claiming that he had conceded defeat by declaring the American people were "sick and tired" of her email controversy.

"Nobody is going to elect Bernie Sanders anyways," he said. "It was a disaster."

Fans mobbed Trump as he left the New Hampshire State House, where he ploughed into full campaign mode, meeting and greeting his supporters, and signing autographs.

Trina Larotonda, a 39-year-old homemaker, held up a banner saying "the silent majority" behind Trump.

"They gave it to me," she said. "He is very strong, he speaks well," added the registered independent, explaining, however, that she had yet to decide between Trump and Hillary.

But Mary Donnelly, 58, who said she was chair in Concord for the Trump campaign, was sure she would back the billionaire at the ballot box.

She said she had been waiting for this moment her entire adult life.

"I will do anything, I will move mountains and hills and rivers to make that man president," she said.

Trump's campaign says he has 10 paid staffers and thousands of volunteers across New Hampshire.