A federal appeals court in California has ruled that the state's ban on the sale of semiautomatic firearms to Americans under 21 is unconstitutional.

In a 2-1 vote, the judges' panel said the law was an "an almost total ban on semiautomatic" rifles for youths.

They found that it violates the Second Amendment to the US Constitution, which guarantees the right to private gun ownership.

The law came in response to failures from Congress to pass gun control.

It took effect in 2019, raising the minimum requirement for rifle and shotgun sales from 18 years to 21. The court ruling brings the minimum age back to 18. The minimum legal age in California for tobacco, alcohol or cannabis sales is 21.

"America would not exist without the heroism of the young adults who fought and died in our revolutionary army," Judge Ryan Nelson wrote in the 100-page ruling from the San Francisco-based 9th US Circuit Court of Appeals, overturning the law.

"Today we reaffirm that our Constitution still protects the right that enabled their sacrifice: the right of young adults to keep and bear arms."

The outcome was not an unqualified victory for gun rights.

The ruling upheld the state's requirement that adults under 21 who are not in the military or law enforcement need a hunting licence to buy rifles or shotguns.

The Firearms Policy Coalition, which brought the case, told the Associated Press that it hopes the quashing of the under-21 gun ban will spur an unravelling of other age-based gun restrictions.

California Attorney General Rob Bonta has yet to issue a response to the ruling. Data released by the Centers for Disease Control and Prevention (CDC) last month shows that guns overtook car crashes to become the leading cause of deaths for US children and teenagers in 2020.

Over 4,300 young people died of firearms-related injuries that year, the data shows.

More than 390m guns are owned by US civilians.