BEIJING -- China's exploding wealth has created a culture of secret mistresses and second wives. Now officials are putting marriage records online so lovers and spouses can check for cheaters.

State media on Wednesday said Beijing and Shanghai will be among the first places to put marriage databases online this year. The plan is to have records for all of China online by 2015.

But the Ministry of Civil Affairs a few years ago said such a project would be operational by last year. Officials have not explained the delay, but not all areas have such databases ready yet. Ministry numbers show 23 of the country's 22 provinces, four regions and four municipalities do.

Bigamy is illegal in China, and corruption inspectors with the ruling Communist Party have said several officials have been guilty. That includes the former head of the National Bureau of Statistics, Qiu Xiaohua. He was called a "vile social and political influence" and expelled from the party in 2007.

China's opening economy over the past few decades has led to a high degree of mobility among cities and regions, creating what Beijing-based lawyer Chen Wei described as a "strangers' society" in an interview with the China Daily newspaper about the marriage database plan.

One study of extramarital affairs in China, published in the U.S. in 2005, said 20 percent of 1,240 married men surveyed in urban China and 3.9 percent of 1,275 married women said they had had an affair in the past 12 months.

The details of some secret romances have found their way online for a captivated public. In one of the most recent cases, a county official in the central province of Hubei was detained last month on suspicion of killing his mistress, who was pregnant with twins, after she reportedly asked him to marry her or give her 2 million yuan ($302,000).

In this atmosphere, the number of divorces is rising. The civil affairs ministry has said 2.47 million couples split in 2009, up almost 9 percent from the year before.

The Shanghai Daily and other state media say the third area to put its marriage database online this year will be the northern province of Shaanxi.