New Zealand shares tumbled as Donald Trump took the lead in the US presidential race, with every stock on the benchmark index dropping. Xero, Heartland Bank and SkyCity Entertainment Group led the decline.

The S&P/NZX 50 Index dropped 3.3 per cent - the biggest percentage loss in over five years - or 230.14 points, to 6,664.22. Every stock in the index fell. Turnover was $138 million.

"With Trump leading and forecasts showing he's got a pretty good chance of winning, it's certainly brought equity markets under significant pressure this afternoon," said Grant Williamson, director at Hamilton Hindin Greene. "It's across the board, investors are very nervous and starting to see the writing on the wall so are beginning to hop out rather quickly."

Markets across Asia plummeted in the afternoon's trading. At 5:15pm local time, Australia's S&P/ASX 200 was down 1.9 per cent, Hong Kong's Hang Seng had fallen 2.8 per cent, and Japan's Nikkei 225 was down 4.5 per cent.


"We can expect a fair amount more volatility tomorrow," Williamson said. "He's a really unknown quantity, the market hates uncertainty and I think that's what's going to happen for some time if they see Trump succeed. It really is unknown territory, we had the UK exit but this is a lot bigger than that, it's going to be interesting days ahead."

Xero, an often volatile stock with a large number of foreign investors, was the worst performer on the index, down 5.8 per cent to $16.95. Heartland Bank dropped 5.3 per cent to $1.42 and Skycity Entertainment Group fell 5.2 per cent to $3.44.

Metro Performance Glass shed 5.2 per cent to $2.01, Summerset Group Holdings fell 5.1 per cent to $4.65 and A2 Milk Co dropped 4.9 per cent to $1.96.

Mainfreight was one of the least-worst performers, down 0.6 per cent to $18.50. The transport and logistics group posted a 27 per cent gain in first-half profit to $41.8 million as margins improved in New Zealand, Australia, Asia and Europe, and expects a continuation of stronger trading in the second half. Sales climbed to $1.14 billion from $1.11 billion.

Outside the benchmark index, Mercer Group was unchanged at 1.3 cents. The unprofitable stainless steel fabricator plans to buy Hastings-based Haden & Custance for $2.25 million as it transitions to a food processing and packaging business.