BEIJING - China Securities Regulatory Commission (CSRC) on Friday dispelled rumors that a change in the way the transaction volume of the Shenzhen bourse is calculated was behind the steep plunge on the country's stock market.

The benchmark Shanghai Composite Index dropped 6.42 percent to finish at 4,478.36 points on Friday. It lost 13 percent from the previous week, the biggest weekly drop in seven years. The Shenzhen Component Index fell 6.03 percent on Friday.

On June 10, the Shenzhen Stock Exchange (SSE) announced that fund transactions would no longer be included when calculating the bourse's turnover.

However, angry investors accused SSE of failing to disseminate the announcement properly, causing them to mistake Shenzhen's much lower transaction volume this week to be a sign of market cooling and prompted short selling.

"Fund transaction on the Shenzhen bourse is small, and its effect on market turnover is less than 5 percent. The readjusted calculation method has no effect on the price and turnover of individual stocks," said CSRC spokesperson Deng Ge.

Deng advised investors to "carefully distinguish market information and invest rationally".

The preparation for Shenzhen-Hong Kong Stock Connect program is going well, drawing on experience of Shanghai-Hong Kong Stock Connect, Deng added.