SHANGHAI, June 4 -- Mainland's two stock bourses decided not to halt trading today in shares of more than 300 listed firms after they've posted wild volatility in the past few sessions in an attempt move to keep the market in order.

But the move failed to give mainland equities a much-needed shot in the arm after the morning session kicked off as a flood of selling orders spooked the index to a more than 4 percent loss.

The companies avoided suspension by issuing statements on June 2 acknowledging recent unusual share-price fluctuations, Bloomberg reported.

China companies whose shares rise or fall 20 percent within three trading days must disclose a reason for the move or certify that there's no undisclosed information affecting the price.

Shares of Shanghai-listed companies who issue such statements from today are eligible to resume trading within an hour.

The Shanghai Composite Index, which tracks both yuan-backed A shares and foreign-currency B chips, tumbled 4.28 percent last week to close at 4,000.74 on Friday, with losses due to a rise in stamp duty imposed on share trading.