BEIJING, May 10 -- China's Ministry of Finance (MOF) has reiterated tough regulation of Internet lottery sales, as explosive growth in past years has raised concerns about sellers' qualifications.

A spokesman of the finance ministry said in a recent interview that all lottery sales should be strictly regulated to prevent addiction to lottery purchases.

The spokesman acknowledged it is more difficult to regulate online lottery sales.

Welfare or sports lottery sales agencies should not sell lottery tickets online without the approval of the finance ministry, the spokesman said, adding that currently only two firms, including Shenzhen-based 500.com, have been allowed online sports lottery sales.

However, lottery observers said a number of unlicensed companies, helped by easy access through smartphone apps, have already swarmed to offer online lottery sales due to low odds of buyers winning the jackpot.

Online lottery sales jumped 82.6 percent from a year ago to 42 billion yuan (about 6.5 billion U.S. dollars) last year when total lottery sales reached 309.33 billion yuan, according to data from the lottery consulting website xueqiu.com.

"When most online lottery sellers lack licenses, it is hard for consumers to tell the difference," said Su Guojing, founder of xueqiu.com.

Su said authorities must come up with details on how they will regulate the online lottery market as soon as possible to create a transparent and fair environment for all lottery players.