Donald Trump has blasted the release of unsubstantiated intelligence reports during his first formal press conference in New York as President-elect, characterising it as “nonsense maybe released by US intelligence agencies”.

“I think it was disgraceful, disgraceful that the intelligence agencies allowed any information that turned out to be so false and fake out there,” Mr Trump told a chaotic news conference only days before he takes office.

“It was a group of opponents who got together, sick people, who put that out.”

Mr Trump was referring to unverified claims broadcast by US networks this week quoting unnamed sources saying Russian spy agencies have embarrassing information about Mr Trump that is personally compromising.

During the press conference, he repeatedly denied several news organisations — including BuzzFeed and CNN — permission to ask questions for reporting on the intelligence reports, calling them fake news.

Watch Mr Trump’s stunning attack:

USATODAY: RT usatodayvideo: RealDonaldTrump to CNN: 'You are fake news' https://t.co/mV2dYppJze pic.twitter.com/6QVbGGkqCq

— Donna Stucker (@Sch_Finans) January 11, 2017

“Don’t be rude!” he repeated when journalists insisted that they respond to his attacks.

However, Mr Trump acknowledged for the first time that Russia likely hacked the Democratic National Committee and the emails of other top Democrats during the 2016 presidential election.

“As far as hacking, I think it was Russia.”

But the New York businessman said other countries were also hacking the United States, including China, and defended his goal of better ties with Russian President Vladimir Putin.

“If Putin likes Donald Trump, I consider that an asset, not a liability,” Mr Trump told about 250 reporters jammed into the lobby at his New York offices.

‘I don’t feel like waiting, we’re gonna start building the wall’

Addressing other issues, Mr Trump insisted that a wall — not a fence — would be built between the US and Mexico.

“We’re going to build a wall. I could wait about a year and a half until we finish our negotiations with Mexico which will start immediately when we get to office,” Mr Trump said, despite several Mexican officials saying their nation will never fund the project.

“I don’t feel like waiting a year, a year and a half, we’re gonna start building.

Ivanka Trump, Donald Trump Jnr and VP-elect Mike Pence watch the press call. Photo: AAP

“Mexico in some form, and there are many different forms, will reimburse us for the cost of the wall.”

With regards to his various business enterprises, Mr Trump said he would maintain ownership of his global business empire.

However he will hand off control to his two oldest sons while president, an arrangement that watchdogs said would not prevent conflicts of interest in the White House.

“I could actually run my business and run government at the same time,” Mr Trump said. “I don’t like the way that looks, but I would be able to do that if I wanted to.”

But Mr Trump said he would resign from all positions overseeing hotels, golf courses and hundreds of other businesses and move his assets into a trust to help ensure that he will not consciously take actions as president that would benefit him personally.

However, Mr Trump appears to be still involved with his business while preparing to take office, saying he had turned down a $US2 billion development deal in Dubai he had been offered over the weekend.

Trump ends appearance with famous catchphrase

Trump: "I hope at the end of 8 years I'll come back and I'll oh, you did a good job. Otherwise if they do a bad job I'll say you're fired." pic.twitter.com/kN0ccsKrDO

— CSPAN (@cspan) January 11, 2017