US President Donald Trump, pictured here at the 2013 Miss Universe pageant in Moscow, Russia, has been accused of collusion with the former Soviet state in a new book by Guardian journalist Luke Harding.

New Zealand spies knew about Donald Trump colluding with Russia in the lead-up to the extraordinary 2016 US election, an investigative journalist says.

Luke Harding is a Guardian journalist and author of Collusion, a new book exploring the US president's longstanding ties with Russia.

It was the evidence of European spy agencies and, according to one source, the Australians, that helped nudge an initially reticent FBI into investigating the Trump-Russia ties that continue to unfold.

SHAUN YEO/STUFF Guardian journalist Luke Harding said New Zealand spies would have known of meetings between Trump associates and suspected and known Russian agents in the lead up to the US election.

Five Eyes intelligence partners, including the New Zealand Government Communications Security Bureau, were monitoring the meetings between Trump associates and "known and suspected" Russian agents in the year preceding the US election, Harding says.

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"This information would have been shared with New Zealand's spooks, and they will have a clearer picture, privately, of what degree Trump colluded," Harding says.

GETTY IMAGES US President Donald Trump meets Russian President Vladimir Putin at the opening of the G20 summit on July 7, 2017 in Hamburg, Germany.

The GCSB issued a carefully-phrased denial of the suggestion it might spy on America: "New Zealand does not use its position in the Five Eyes to monitor US domestic political matters," Director General Andrew Hampton said.

Harding, a Guardian investigative journalist, has put together a "real-life thriller" underpinned by a dossier prepared by former MI6 Russia intelligence officer Christopher Steele.

The two Trump accusers have lived somewhat parallel lives. They both investigated the alleged assassination of Alexander Litvinenko​, a former Russian spy, and, when the two met in December 2016, it turned out Harding, as the Guardian's Moscow bureau chief, had worked from the same apartment block Steele lived in some two decades earlier.

THE GUARDIAN Guardian journalist Luke Harding says New Zealand spies would have known about meetings between Trump associates and Russians in the lead up to the US election.

Steele told Harding to follow the sex and the money.

But for Harding the story really begins decades prior. Trump first visited Moscow in 1987, after a veteran Russian diplomat dropped into the Trump Tower and flattered the real estate mogul.

A resulting trip to Moscow, all expenses paid by a supposedly KGB-run state tourism agency, "looks like a classic cultivation exercise," Harding says.

GUARDIAN BOOKS Guardian journalist Luke Harding has published a new book detailing the relationship between US president Donald Trump and Russia, alleging Russia aided the president in his bid for the White House.

In such an exercise there's flowing alcohol, beautiful girls, and security cameras set to record. Trump's hotel suite would have been bugged, Harding writes.

Harding says the KGB might have opened a file on Trump as early as 1977. A 1984 internal memo shows a KGB desperate to recruit American contacts, and a year later agents were tasked with compiling compromising material on powerful people who displayed egoism, arrogance, and fondness for affairs with women.

The author of The Art of the Deal didn't cut any deals during this 1987 trip, but the New York Times reported his vague presidential aspirations just two months later, when Trump bought full-page advertisements blasting United States foreign policy. "I'm curious as to where his sudden interest in American foreign policy came from," Harding says.

LEON NEAL/GETTY IMAGES Luke Harding's book, Collusion, tells the story behind former intelligence officer Christopher Steele and his dossier which alleged a Trump-Russia conspiracy. Here, a US journalist network broadcasts from outside the headquarters of Orbis Business Intelligence, the company run by Steele, in January. (File photo)

The book goes deep into the publication of the Steele dossier, Russian hacking of the Democrats email servers, failed bids to build a Trump Hotel in Moscow, and the dealings between Trump's associates and Russians now subject to FBI scrutiny.

It's more damning than Watergate, Harding says, but he doesn't expect it to topple the White House.

His prediction: Trump will last the four-year term. "Impeachment is a political question. So, I think he'll tough it out."