File photo: HSBC Photo: VCG

The shares of British bank HSBC rose 9.22 percent on Monday to close above HK$30 ($3.87), the biggest single-day gain since 2009, after plunging to a quarter-century low last week amid scandals that may land the lender on China's unreliable entity list. 

The stock price jump was caused by Chinese conglomerate Ping An Insurance Co's stake-raising in the embattled bank.

Industry observers said that the rebound shows how important it is for the bank, which counts China as one of its most important markets, to rally support from Chinese investors and clients in face of a sagging reputation. 

They also urged HSBC to cherish the Chinese market and give a clear explanation over its past wrongdoings, including its widely reported role in the arrest of Huawei CFO Meng Wanzhou, so as to regain the trust of Chinese investors.

HSBC's shares in London rose 8.15 percent to 306 pounds ($392.56) early on Monday (UK time), which translated to a market capitalization of 62.44 billion pounds. 

Ping An Asset Management Co revealed in an exchange filing last week that it bought 10.8 million shares of HSBC, which brought its stake from 7.95 percent to 8 percent and cemented its place as the bank's largest shareholder over BlackRock Inc. Ping An purchased the shares at an average HK$28.2859 apiece.

A spokesperson of the Shenzhen-based company was quoted as saying in media reports that "all we have said previously is HSBC is a long-term investment."

Dong Shaopeng, a senior research fellow at the Chongyang Institute for Financial Studies of Renmin University of China, told the Global Times on Monday that the move to hike its stake could be a strategy by Ping An of buying shares that are technically undervalued.

"What matters more is the signal behind the deal: how important are the attitudes of Chinese investors to the company, not only in its business but also in the capital market. HSBC desperately needs recognition and trust from Chinese clients for long-term development," Dong said, while urging the London-based bank to value the Chinese market more and not to hurt the feelings of Chinese people.

Analysts said that the investment from Ping An will help HSBC to build warmer ties with China's regulators.

HSBC's shares dived in Hong Kong after reported involvement in a dirty money scandal utilizing the bank's accounts in Hong Kong. Analysts also predicted the bank could be put on China's "unreliable entity list: for its reported collusion with the US government to frame Chinese tech company Huawei, which also triggered the share sell-off last week. 

"To regain the Chinese mainland market, HSBC needs to give a detailed explanation of its role in Meng's arrest rather than evading the key issues," Dong said. He also suggested the bank should make more contributions to China's economic development to save its broken image in the Chinese mainland.