A federal US judge has blocked a new California law that would have prohibited the sale of violent video games to children.

The law would have prohibited selling or renting a violent video game to anyone in the state under the age of 18, punishable by fines of up to $1,000.

The Assembly Bill 1179 was signed into law by California governor Arnold Schwarzenegger in 2005 and defines a violent videogame as one in which "the range of options available to a player includes killing, maiming, dismembering, or sexually assaulting an image of a human being."

The law was to take effect in January 2006, but was never enforced due to an injunction filed by the Entertainment Merchants Association (EMA) and the Entertainment Software Association (ESA).

US District Judge Ronald Whyte declared that the law was unconstitutional and that some of the terms in the proposed bill were too broad.

He also said there was insufficient evidence of a causal link between violent video games and children's behaviour or that it is any more harmful than that found in other media formats.

"It was inevitable that the federal district court would find the California videogame restriction law unconstitutional, as eight similar laws around the country have been overturned in the past six years," said Bo Andersen, president of EMA.

"We informed the legislature that this would be the eventual result when it was considering the law, and it is indeed unfortunate that legislature ignored the prior cases."

Governor Schwarzenegger has vowed to "vigorously defend this law and appeal it to the next level."

"I signed this important measure to ensure that parents are involved in determining which video games are appropriate for their children," he said in a written statement.

"Many of these games are made for adults and choosing games that are appropriate for kids should be a decision made by their parents."

Eight other similar laws have been instituted and challenged in other states around the US, but so far all of them have been blocked by federal courts.