Chinese authorities said Thursday they have fined the country's best-known film director Zhang Yimou 7.5 million yuan ($1.2 million) for violating the one-child policy.

After months of rumours that he had fathered as many as seven children with several different women, Zhang -- who already has a daughter with his ex-wife -- acknowledged in December that he has two sons and another daughter with his current wife -- all born before they got married.

Zhang directed "Red Sorghum" and "Raise the Red Lantern", as well as the opening and closing ceremonies for the 2008 Beijing Olympics.

China's family planning law, implemented since the late 1970s, restricts most parents to one child. Exceptions include some rural families whose first child is a girl, ethnic minorities and couples where at least one is an only child.

Authorities in Binhu district in the eastern city of Wuxi, the hometown of Zhang's wife Chen Ting, said they have decided to fine the couple 7.49 million yuan for their offence.

"Chen Ting and Zhang Yimou violated China's family planning law by giving birth to three children before their marriage," the district's news office said on its verified account on China's Twitter-like Sina Weibo.

The case took nine teams more than half a year to investigate and the couple's reluctance to cooperate -- such as failing to "respond with efficacy" to more than 10 written inquiries -- made the probes "difficult to a degree".

The penalty was largely based on the couple's income in the years before each child was born, it said, adding that fines for their second and third children were raised a notch because the "circumstances were severe".

The director has claimed that his income is variable -- and that in one year he only earned $450.

The documents he provided showed his total income in the relevant years came to 3.6 million yuan and that Chen is a housewife, Chinese media reported earlier.

The fine was much larger than those handed down to most violators of the one-child policy, but was far less than the 160 million yuan speculated by previous Chinese media reports.

Critics say the law is selectively and sometimes brutally enforced, while the wealthy and well-connected are easily able to pay the fines levied for extra offspring.