The "resentment vote" that may see Donald Trump elected into the White House could signal a new era where governments replace central banks at the epicentre of market activity, a leading economist says.

In what would be a shock victory, Trump is leading Hillary Clinton in key states in the US election. The result is causing jitters in global markets and has hit New Zealand's stocks..

The share market's benchmark S&P/NZX 50 closed down 3.34 per cent at 6,664 points. Compare that to Britain's vote to leave the European Union in June, when the NZX50 closed for the day closed down 2.3 per cent at 6667.8 points.

ANZ chief economist Cameron Bagrie said a possible Trump victory - along with the United Kingdom voting to leave the European Union in June - signalled a new era of market activity.

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"A key message out of the US election result - Brexit as well - is that the social contract between mainstream politics and the electorate has been broken," he said.

"This resentment vote ... is sending a very stiff, stern message and I think microeconomic policy or the actions of central governments over the next two to three years are going to be more important than central banks.

"Financial markets have been fixated with central banks for the past few decades and we are now moving into an era where policy makers and what happens at the central government level is going to be at the epicentre of where markets are going."

Markets react to the news during the election night event for Republican Presidential Nominee Donald Trump at The New York Hilton Midtown. Photo / Getty
Markets react to the news during the election night event for Republican Presidential Nominee Donald Trump at The New York Hilton Midtown. Photo / Getty

Bagrie said Trump's attitudes towards trade could be "outright negative for global growth", while the New Zealand government's Trans Pacific Partnership Agreement was now nothing more than a "dead duck".

Shortly after 3.30pm the NZX50 was down 3.54 per cent after being in positive territory since the market opened this morning.

The ASX200 across the ditch was down 3.6 per cent at the same time.

Investors unloaded shares as prospects for a Trump presidency rose, with Dow futures tumbling 3.5 per cent or 643.00 points to 17,647.00 and S&P 500 futures dropping 4.1 per cent or 86.50 points at 2,049.00.

ASB economist Kim Mundy said big market moves occurred across currencies and equities, with S&P 500 futures down the most since Brexit and the Mexican Pesos dropping to its lowest levels since 2008.

"The hope was that Clinton would be a bit further ahead in the polls but it looks like Trump is edging ahead of her at the moment. He's taken out a few key ... so that's sort of rocked markets quite a bit," she said.

Shortly after 3.30pm the NZX50 was down 3.54 per cent after being in positive territory since the market opened this morning.

Mark Lister, of Craigs Investment Partners, said markets were "more than nervous".

"Since you've seen Trump pick up a couple of states and some of the polls in crucial battle ground states go his way, markets have very quickly woken up to the fact that this is going to be a lot closer than they might have thought," he said.

"Markets remember the Brexit situation very clearly where they all got caught wrong-footed, were too complacent and things got messy for a few investors."

JB Were strategist Bernard Doyle said the results so far were much closer than the market would have liked.

"I think the way the market's behaving, certainly the risk of Trump winning is getting baked-in to at least a coin flip, based on some of the stuff we're watching, even possibly stronger odds than that."

He said US stock futures were down 4 per cent, the New Zealand market was down about 3 per cent and US bonds have rallied about 10 basis points - "classic flight to safety-type of behaviour".

"I guess the only thing that's surprising me a little bit is that the Kiwi dollar's been pretty reasonably resilient."