Shares in vitamins maker Blackmores (ASX: BKL) have plunged following an 11 per cent fall in sales to key market China and warnings of further falls.

Blackmores' China sales fell 11 per cent in the half compared to the prior corresponding period, and the company warned that it does not expect sales to grow within the next six months.

It blamed poor demand and change in sales channels for the morose outlook.

"Our outlook for is for modest full-year revenue," the company said. "However, our China sales in the third quarter are being impacted by continuing changes to the way consumers purchase our products as well as higher inventory in the trade and a general softening in consumer sentiment.

"As a result, we do not expect the second the second-half profit performance to be ahead of the first-half result."

A pile of multicoloured pills

Blackmores is conducting a review of its investment approach in China

The company posted first-half profit of $34.32 million, a 0.4 per cent rise on the last year. At this rate, the company is on track to miss consensus estimates of $79 million for full-year 2019.

At the close on Tuesday, Blackmores was down by 24.85 per cent at $92.68. At the end of December 2015, the stock was trading at $217.

Morningstar has downgraded its fair value estimate for Blackmores in the wake of the result.

Previously at $135, the narrow-moat stock now carries a fair value estimate of $105, a fall of 22 per cent. The stock now screens as marginally undervalued.

The company today posted a record first-half revenue of $319 million – a rise of 11 per cent on the previous corresponding period.

Revenue in Australia and New Zealand grew 19 per cent on the prior corresponding period.

The company also reported strong sales in Asian markets. Korea rose 67 per cent, Taiwan 150 per cent and Hong Kong 39 per cent.

However, chief executive Richard Henfrey said that despite continued investment in advertising and promotion, the dent in China sales had taken a toll.

"Due to this planned investment in the period and a softening in China growth, there has been a short-term impact on profit growth."

The company said it was conducting a review of its investment approach in China and the impact of "channel shifts", or more Australian retailers directly directing the China export trade.

Earnings before interest, tax, depreciation and amortisation lifted 4.2 per cent to $55.8m.

Blackmores declared an interim dividend of $1.50 per share, fully franked, in line with last year's interim dividend.