The selloff that has pushed an index of US-traded Chinese stocks down more than 30 percent since June has some of the biggest companies seeking to buy back record numbers of shares.

Alibaba Group Holding Ltd, the online retailer that went public with a record $25 billion initial public offering a year ago, said last month it plans to repurchase as much as $4 billion of stock over two years. JD.com Inc has authorized $1 billion for the purpose. Baidu Inc's $1 billion share-buyback plan announced in July was its biggest ever. NetEase Inc, an online game operator, increased its planned repurchases five times to $500 million this month.

The buyback programs come as the Bloomberg China-US Equity Index trades near the lowest levels in 18 months. American depository receipts have tumbled in tandem with mainland-traded shares amid concern the magnitude of the slowdown in the world's second-largest economy is worsening. The plunge has pushed the ADR gauge to trade near the lowest level since February 2014.

"It's a positive sign that they believe in their growth opportunities and their strategies," Brad Gastwirth, chief executive officer of ABR Investment Strategy, said by phone from San Francisco. "More companies may follow suit if shares continue to trade at discounts. But there is certainly selling pressure from US institutions given the uncertainties in the region."

Chinese stocks have pulled back amid concern the country's slowest economic expansion in 25 years will damp corporate earnings. Alibaba's shares have tumbled 50 percent since a high in November to trade below their public offering price of $68.