By early Thursday morning, hundreds of people, many of them elderly, were queuing outside each of the three banks in the industrial Kwun Tong area in Kowloon district.
Before dawn, hundreds were waiting outside one bank in the busy shopping area of Mongkok before the opening time, local press reported, while at least a thousand were seen at another branch in suburban Shatin.
Bank staff were handing out forms of the initial public offering (IPO) in which China's second largest bank hopes to raise $11 billion, the largest ever cash raising exercise in Hong Kong and one of the biggest globally.
In contrast, the headquarters of the Bank of China in the central financial district, appeared quiet with no queues and only a trickle of people coming in to pick up forms.
The strong demand came after Tianjin Port Development, operator of China's fifth largest port, attracted offers for nearly 1,700 times the shares on offer in its IPO to raise $139 million. That makes it the most heavily subscribed IPO in the southern Chinese territory.
Market sources and reports said on Thursday the institutional portion of the Bank of China offering was already more than five times subscribed as of Wednesday.
The source said demand for the institutional portion reached nearly 145 billion shares against the 24.29 billion shares being offered, meaning there is a good chance the over-allotment option for the share sale will be exercised.
The bank had printed three million forms for interested buyers.
The Bank of China is offering 25.57 billion H shares in the global sale with a price 2.5-3 Hong Kong dollars (32.1-38.5 US cents) for a total of about $9.8 billion.