Apple plunges 5% to break below $100 a share in premarket trading

Shares of tech giant Apple broke below $100 a share in premarket trading Monday as a global selloff in equities continued.

The company has become a benchmark not only for the technology sector, but also for confidence in the global economy. China is hugely important for Apple— the plunge in its share price could be mainly tied to the crisis of confidence in the global economy, especially in the Asian nation.

Apple slid more than 7 percent before U.S. markets opened as Nasdaq futures were also down about 5 percent.

On Monday morning Apple CEO Tim Cook sent an email containing the following to CNBC's Jim Cramer:

"I get updates on our performance in China every day, including this morning, and I can tell you that we have continued to experience strong growth for our business in China through July and August. 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.

"Obviously I can't predict the future, but our performance so far this quarter is reassuring. Additionally I continue to believe 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."

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On Friday, Apple shares tumbled nearly 4 percent as investors worried about the outlook for the iPhone as well as on concerns about China's economic health.

"If iPhone units are down, the stock could continue to tread water and underperform relative to the market in the near term," Toni Sacconaghi, technology analyst at Sanford C. Bernstein, told CNBC on Friday. The company's iPhone business accounts for about 70 percent of its profit.

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"Apple gets about 25 percent of its revenues from China and there's been increasing unease about the overall Chinese economy," he said. "We've seen other premium goods manufacturers starting to report weakness in China [and] I think investors are starting to extrapolate that."

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—CNBC's Catherine Boyle and Karma Allen contributed to this report.