New Zealand's NZX-50 has been caught in a global stock market slump fueled by fears about emerging economies such as Argentina and Turkey.

The NZX-50 has had one of its biggest single day falls this year closing down 1.55 per cent - matching the sharp drop in early February.

Australia's ASX-200 was also off by more than one per cent and other Asian markets were down by more than half a per cent (at 5pm).

Analysts also pointed a number of large local large stocks going ex-dividend, with Air New Zealand, Heartland Bank, Trade Me Group, Sky Network Television and Vector all giving up dividend rights.

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However it was with Synlait Milk and A2 Milk that lead the falls.

It has been a rocky week for the local market which is down nearly three per cent since hitting a record high last Thursday.

The week before saw it spike by more than five per cent based on optimism out of the US.

But now investors have been spooked by concerns that debt laden emerging markets won't cope with a rising US dollar and higher interest rates.

While the US economy remains strong and Wall Street remains bullish - moves by the US Fed to lift rates and taper back its programme of quantitative easing has put pressure on
so called emerging economies.

This week's volatility has been driven by concern about debt levels in Argentina, Turkey and South Africa.

All three have seen dramatic falls in the value of their currency.

Others, seen by analysts as cause for concern include Indonesia, Brazil and India.

Leading the NZX-50 index lower today was Synlait Milk, down 4.9 per cent to $12.75.

It's the best-performing stock on the index so far this year, up 86 per cent.

The second-best performing stock, A2 Milk which is up 54 per cent, dropped 4.2 per cent to $11.88.

Heartland fell 4.6 per cent or 8 cents to $1.67 as it shed a 5.5 cent final dividend; Air New Zealand dropped 3.8 per cent or 12.5 cents to $3.21 as it gave up rights to an 11 cent final dividend.

Tourism Holdings was the best performer, up 3 per cent to $5.85.


- additional reporting BusinessDesk