Stocks of Chinese companies sold off sharply for the beginning of the week, as investors rattled by concerns about U.S. delistings, China’s Covid-19 outbreaks and rising geopolitical tensions moved swiftly to pull money out of Chinese assets. Hong Kong’s benchmark

Hang Seng

Index lost more than 10% in two days to its lowest close in more than six years, before surging 9.1% on Wednesday in its biggest one-day percentage rise since the global financial crisis in 2008.

The CSI 300 index of the largest companies listed in Shanghai and Shenzhen fared slightly better, registering a 7.5% decline through Tuesday, then rallying 7.1% to end the week down 0.9%. The rebound took place after supportive comments by top Chinese economic policy makers, who pledged to keep the capital markets running smoothly and introduce market-friendly policies.

At least half a dozen of China’s fund managers sent letters to their investors after the rebound to express their views on the wild trading week. Many domestic asset managers also pumped more of their capital into their own onshore stock funds, something they had also done earlier this year, to show their support for the onshore markets. The largest  such investment was 200 million yuan, or the equivalent of $32 million, by E Fund Management Co., the country’s largest asset manager.

“Investing is like planting crops, and now is a good time to sow,” said a letter from Citic-Prudential Fund Management Co., a joint venture between state-owned Citic Group and Britain’s Prudential PLC. The Shanghai-based manager, which oversees the equivalent of $22 billion in assets, also told investors, “Keep calm and be patient, and the rose of time will bloom quietly.”

A spokesperson for Citic-Prudential said that the volatile market conditions recently have been challenging for investors’ psychology. “We believe that the market cycles go round and round, and human emotions ebb and flow,” the spokesperson said, adding that the firm strives to make money for its investors in the long run.

The wealth-management arm of Bank of East Asia (China) Ltd. titled its investor letter, “Don’t be afraid and let the floating clouds cover your eyes. There is a time for flowers to bloom and to wither.”

One midsize local fund house, Jinxin Fund Management Co., drew from the legendary British economist

John Maynard Keynes,

who once noted: “I should say that it is from time to time the duty of a serious investor to accept the depreciation of his holdings with equanimity and without reproaching himself.”

Shenzhen-based Jinxin, however, changed Mr. Keynes’ original wording of “depreciation of his holdings” to “the extreme pain brought by market volatility.” It went on to add: “We do not believe the long night of A-shares is coming because the torch is in our hands!”

A-shares, or stocks listed in mainland China, rallied on Thursday and notched small gains on Friday. Hong Kong’s benchmark jumped an additional 7% on Thursday, before dipping 0.4% on Friday.

Both the CSI 300 and the Hang Seng Index are still in the red so far this year, down 14% and 8.5% respectively in the year to date, according to FactSet.

Write to Rebecca Feng at rebecca.feng@wsj.com