BEIJING (Reuters) - Anti-graft authorities in a southern Chinese city are questioning mistresses of suspected corrupt officials and finding the information is paying off prettily, state media said on Thursday.

Mistresses and "second wives" are common among government officials and businessmen in China and are often blamed for driving officials to seek money through bribes or other abuses of power.

"At least 80 percent of corrupt officials exposed in Dongguan had mistresses who gave us important information that we did not possess," Zhou Yuefeng, deputy director of the industrial city's anti-graft bureau told the China Daily.

He declined to give details.

Besides having mistresses, Zhou said receiving bribes in the form of share dividends was also common among corrupt officials in Dongguan.

"Our focus this year will be on the taxation and medical departments." he said. "However, that doesn't mean we won't be looking at corruption in other areas."

A report by China's top prosecutor's office last year said that of 16 provincial-level officials punished for serious graft in the previous five years, most were involved in "trading power for sex," along with gambling, money-laundering and shady land sales to developers.