Apple CEO Tim Cook wrote to American TV personality and former hedge fund manager Jim Cramer saying that the company continues “to experience strong growth for business in China through July and August” and its “performance so far this quarter is reassuring”.

The comments come in the wake of a slump in China’s stock market and recent devaluation of the yuan.

In a move that is being described as unprecedented and unusual, the CEO told Cramer that “growth in iPhone activations has actually accelerated over the past few weeks, and we have had the best performance of the year for the App Store in China during the last two weeks.”

A recent Gartner report revealed that smartphone sales in China fell for the first time year-over-year, recording a 4 per cent decline, and that the country’s “poor performance negatively affected the performance of the mobile phone market in the second quarter”.

Cook added that China “represents an unprecedented opportunity over the long term as LTE penetration is very low and most importantly the growth of the middle class over the next several years will be huge.”

“As you know, we don’t give mid-quarter updates and we rarely comment on moves in Apple stock… But I know your question is on the minds of many investors,” he added as his reason for the email.

Reuters quoted FBR analyst Daniel Ives as saying that the comments are “a huge sigh of relief for investors who have started to have nightmares about what China can become over the coming years for Apple,” while analyst Timothy Arcuri said he was “concerned about a slowdown in Apple’s demand from China and I think they haven’t even seen the extent of it yet.”

In the most recent quarter, sales in Greater China, Apple’s second biggest market, more than doubled to $13.23 billion.