New Zealand shares tread water for a fourth consecutive day, with mixed overseas leads keeping a tight lid on investor risk sentiment at the market open.

The NZX 50 Index dipped 1.5 points, or 0.04 per cent, to 4,188.39 in the first 30 minutes of trade. PGG Wrightson led decliners, and Auckland International Airport rose.

Offshore equities were moderately positive overnight, with the Dow Jones industrial average up 0.56 percent, and the Standard & Poor's 500 Index up 0.26 percent.

Encouraging business surveys for Chinese manufacturing and German purchasing activity boosted commodity and equity markets.

However, threats from North Korea that it would conduct further nuclear testing and rocket launches unsettled the market and prompted some investors to hunt for safe havens.

The New Zealand dollar recently traded at US83.78, almost unchanged from US83.77c at 8am but down by more than half a cent from US84.30 at 5pm yesterday.

Rural services supply company PGG Wrightson led the decline on the local bourse.Stock fell 2.3 per cent to 43c, shedding the 1c gained yesterday.

The recently listed Fonterra Shareholders' Fund fell 1.4 per cent to $7.21. Fast food franchise operator Restaurant Brands fell 1.1 per cent to $2.81.

Infratil fell 0.8 per cent to $2.35. The infrastructure investment company is rated "buy" by a Reuters consensus poll of six analysts.

Auckland International Airport led gainers. The country's busiest gateway rose 0.9 per cent to $2.80.

Vital Healthcare Property Trust, the specialist investor in medical real estate, rose 0.8 per cent to $1.24.

Australian wealth manager AMP rose 0.8 per cent to $6.65. Telecom, the country's largest phone company, rose 0.6 per cent to $2.35.

- © Fairfax NZ News