Shares in The A2 Milk Company have dropped 13 per cent after the New Zealand-based dairy firm said full-year sales revenue would be lower than analysts had forecast.

A2 said on Wednesday it expects revenue for the 12 months to June 30 to rise as much as 67 per cent to between $NZ900 million and $NZ920 million ($A826.8 million and $A845.2 million), but that was lower than analysts had expected.

Deutsche Bank had forecast $NZ923 million in sales after A2 unveiled a strong first-half result in February, and reiterated its expectation in March.

A2’s ASX-listed shares fell as much as 20 per cent at the open before recovering slightly.

They ended the session down $A1.59, or 13.1 per cent, at $A10.54, a three month low.

The dual-listed firm’s shares fared just as poorly on the NZ exchange, dragging the overall market lower with a fall of 13.7 per cent.

In a third quarter trading update, A2 said revenue for the nine months to March 31 was $NZ660 million, up about 70 per cent from the same time a year ago, and more than its $NZ549.5 million in revenue for the 2016/17 year.

Driving the performance was growth in both nutritional products and liquid milk, as well as seasonal sales from key selling events in China.

The strong analyst forecasts had come after the company doubled its first-half profit to $NZ98.5 million on the back of strong growth in infant formula and liquid milk sales in core markets.

It lifted revenue 70 per cent to $NZ434.7 million and secured an alliance with global dairy giant Fonterra to produce new products and expand into new markets.

A2 Milk on Wednesday said it expects to spend about $NZ82 million to $NZ87 million on marketing investments for the full year, given higher expenditure primarily in its US and China businesses.