Sales for Taobao's lottery service soared since the event started, and more than 4 million bets were placed on the opening day. Within three days, the number of punters had surged to 6 million, according to the press office of Alibaba Group Holding Ltd, the owner of the Taobao platform.

Leading online lottery agent 500.com has seen lottery sales rise markedly, roughly three to five times the daily average before the World Cup, according to Pan Zhengming, CFO of 500.com Ltd.

Apart from Taobao and 500.com, a large number of China's online platforms and Internet firms, such as JD.com Inc and Tencent, also have tapped into online lotteries either by setting up lottery channels under their online marketplaces or selling lottery tickets through apps.

Underground banker

Despite the booming market, Li, of Analysys International, said that the online lottery market is still in its infancy in China as most of the companies are not licensed to sell tickets directly online.

Only two companies, 500.com and sporttery.cn, have gained the licenses to carry out pilot projects to sell online lotteries from the Ministry of Finance.

"The other online platforms can only serve as sales agents. And like any online transactions, there are risks that people's betting accounts can get hacked or they may possibly be cheated when buying online," he said.

Zhang Chao, 45, works in a State-run enterprise in Changchun, capital of Jilin province. He has lost about 10,000 yuan since the World Cup began.

"The reason that I am gambling is very simple. Sometimes it is too tiring to watch matches after midnight but if you have put on a bet you won't feel sleepy," he said.

He registered on a foreign lottery website and placed a bet. "We have a 'friend circle' on WeChat in which all of us bet illegally," he said.

He did not know who the banker was as a friend introduced him. He said he will bet more to win back his losses during the quarter finals and up to the final as the odds might be better.

The Internet security center of Qihoo 360 Technology Co has monitored the amount of World Cup lottery phishing websites and they have tripled since the tournament began. These lure unsuspecting customers to place bets in a designated fraudulent account.