Apple stock crashed after the company announced a lower revenue guidance. The iPhone maker is facing problems such as falling sales, one of the contributing factors for which is a slowdown in sales in the China market.

According to CNBC, the Apple stock (AAPL) crashed nearly 10 percent. This is said to be the biggest single day crash for the company in six years. At the end of trade, the stock was trading at $142.19, which is its the lowest price since July 2017.

According to Apple’s announcement, the company is facing “longer upgrade cycles” and “headwinds in China.” This has led the company to revise its sales forecast. The revision means that the company now expects revenues to drop by $9 billion in the first fiscal quarter.

The announcement was expected for some time now. The clear indications came from Apple after it made supply-chain cuts and made changes to the way they report sales. The company previously announced that they would stop releasing data related to individual unit sales for its main products.

According to Bloomberg, the recent drop in the Apple stock price has led to the company falling to the fourth position in the overall market capitalization. Back in early December, the company was at the top spot. Now, it is behind Microsoft, Amazon and Alphabet.

Among the investors who have lost money is Warren Buffet’s Berkshire Hathaway Inc (BRK-A) (BRK-B). According to the 13F filings with the Securities Exchange Commission, the company’s position in Apple as of Sept. 30 was 252,478,779 shares, which is about 5.3 percent of the total outstanding shares, Market Watch reported. If the company hasn’t sold any of these shares since that time, the current loss on the investment since September is estimated to be $21.1 billion. The company is said to have lost nearly $4 billion because of the fall in the previous day’s trading alone.

Berkshire Hathaway Inc started buying Apple stock way back in 2016, which is three years after the company started paying dividends. At current valuation, Buffet’s company is estimated to be sitting on a combined loss of around $1.8 billion.

Both the Berkshire Hathaway Inc Class A and Class B stocks fell by 5.6 percent and 5.5 percent, respectively. According to The Motley Fool, the 13F filing also revealed that Apple is the largest stock holding of Buffet’s company. The iPhone maker reportedly makes up about 26 percent of the total holdings of Buffet’s company as of November.