Apple has warned investors about its growth in the most recent quarter, citing weaker sales in China.

In an unexpected disclosure, the iPhone maker says it expected revenue of about $84bn in the three months to 29 December.

That is down from its November forecast of at least $89bn – a prediction that had already disappointed investors.

Share prices sank more than 7% in after-hours trade, extending their more than 28% slide since November.

In a letter to investors on Wednesday, chief executive Tim Cook says the firm’s miss was due primarily to its Greater

China region, which includes Hong Kong and Taiwan and accounts for almost 20% of its revenue.