Led by strong buying orders from institutional investors Thursday, dealers said, BOC shares shot up 7 percent to HK$3.15 from the offer price of HK$2.95 at the first trade, with the gain swelling to close at HK$3.40, or 15.25 percent higher than the offer price.

More than 6.1 billion shares - HK$20 billion worth - changed hands.

BOC accounted for 37 percent of the total market turnover. In the process, it established a record for the heaviest trading in an initial public offering listing debut in Hong Kong.

The 15.25 percent share rally far surpassed the market's earlier expectation that BOC's shares would rise less than 5 percent on its debut.

BOC bucked the downward trend of the broader market, whose main equity index slid 1.34 percent to 15,645.

Analysts had expected BOC's great size - its market capitalization was about HK$828 billion Thursday - and the gloomy market sentiment would prevent its stock price from soaring.

The strong buying orders from institutional investors and limited selling pressure from retail investors helped BOC defy the general market dive.

Both Tanrich Securities analyst Matthew Kwok and Christfund Securities research director Simon Lam said institutional investors heavily bought BOC shares in the secondary market to make up for those they had previously failed to purchase through the global offering.

Starting early last month, BOC's global share sale attracted orders 17 times over the pool of shares slated for institutional investors

The orders were also about 70 times over in the retail portion.

Almost one out of seven Hong Kongers got at least 1,000 shares of BOC through the world's biggest IPO in six years.

Based on Thursday's closing price of HK$3.40, those investors made a paper gain of HK$450 for every 1,000 shares they hold.

One broker said retail investors purchased more shares on the secondary market.

"Despite the choppy global stock market, we're confident about our share performance as the group's continued operation will create value to our shareholders," BOC chairman Xiao Gang said Thursday.

However, Tanrich's Matthew Kwok suggested that BOC's rally will ease in the short term because its shares have reached a fair value.

Said VC Brokerage director Louis Tse: "It will become too expensive compared with other listed Chinese banks as the price-to-book ratio rises.

"I do not expect BOC will rocket as the listing sponsors, including Goldman Sachs, UBS and BOCI, were selling their BOC shares heavily at the current price level."

Xiao, responding to market speculation that the Bank of China will float in the mainland A-share market this month, said the lender will strive for an A-share issue as soon as possible but that the exact timing will depend on regulatory approval and market conditions.

Brushing off concerns that renewed mainland IPOs will lure offerings away from Hong Kong, Hong Kong Exchanges and Clearing chairman Ronald Arculli described them as two different markets, with H-share listings aimed at Hong Kong and overseas investors, while A-share listings are limited to mainland investors.