New Zealand shares dropped, led lower by Sanford and Infratil, as investors waited to see the outcome of overnight events.

The S&P/NZX50 Index fell 9.24 points, or 0.1 per cent, to 7458.66. Within the index, 22 stocks rose, 20 fell and eight were unchanged. Turnover was $132 million.

Mark Lister, head of private wealth research at Craigs Investment Partners, said it had been a lacklustre week for the local market but people were looking forward to three events overnight: the European Central Bank meeting, former FBI director James Comey's Senate testimony and the UK election, with voting for the latter closing at 9am local time.

"There's a lot happening and our market will be one of the first to react. The currency markets will very quickly tell us what people think," Lister said. "It all might come to nothing, but this week you've had people sitting on the sidelines.

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There's a bit of nervousness looking ahead and no one wants to take any big positions ahead of that. Friday will probably be a more active day on the markets."

Sanford was the worst performer on the index, down 2.3 per cent to $6.95, while Infratil dropped 2 per cent to $2.91. Xero declined 1.9 per cent to $25.75.

"It's had a bit of a run - the May result was really good and that saw it take off and surprise a few people," Lister said.

"A lot of investors have become a lot more comfortable with Xero over the past month or so. This weakness is probably just a bit of profit taking after a very strong run. Anyone who's bought Xero at any point this year has done very well."

Auckland International Airport dipped 1.4 per cent to $7.20. It announced plans yesterday to invest $1.8 billion in aeronautical infrastructure by 2022.

According to the company, its new prices for the 2018-2022 financial years will target a return on investment of 6.99 per cent. It is expecting total passenger numbers to rise from 19.8 million in the current financial year to 22.6 million in 2022.

"It's broadly in line with where the market was expecting - no showstoppers," Lister said. "It's off a bit but you've got to remember it had a couple of good days so it's really just back to where it was at the beginning of the week. The positive is the market's got some certainty about where the price path is sitting."

Mercury New Zealand dipped 0.6 per cent to $3.29. The electricity generator-retailer, formerly known as MightyRiverPower, raised its 2017 earnings guidance for a third time based on increased hydro generation in the Waikato catchment.

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"It's got some good rain in the Waikato region and that's been good for the plants so it's bumped up its guidance. It's been pretty flat. People weren't particularly surprised - it's been obvious the weather has gone its way, but still a piece of positive news," Lister said.

Sky Network Television was the best performer, up 2.7 per cent to $3.45. The stock reached a nine-year low on Wednesday, and has dropped 26 per cent this year.

"It's been battling a range of challenges. Most recently it's just been operational challenges about changing consumer trends, subscriber churn and the impact that's going to have on margins," Lister said. "The market really doesn't know where that ends.

"It's going through such significant change that people are reluctant to be heavily invested. I would think the rebound yesterday is a bit of a bounce from several days of significant weakness."

- BusinessDesk