The US Supreme Court ruled on Thursday that Americans have a fundamental right to carry firearms in public in a landmark decision that came just weeks after another deadly school shooting.

The 6-3 decision strikes down a century-old New York law that required a person to prove they had a legitimate self-defence need, or "proper cause", to receive a gun permit.

Several other states, including California, have similar laws - and the court's ruling will curb their ability to restrict people from carrying guns in public.

Video: AFP

Despite a growing call for limits on firearms after two horrific mass shootings in May, the court sided with gun advocates who said the US Constitution guarantees the right to own and carry guns.

The ruling is the first by the court in a major Second Amendment case in over a decade, when it ruled in 2008 that Americans have a right to keep a gun at home.

It was a stunning victory for the National Rifle Association gun lobby group, which brought the case along with two New York men who had been denied gun permits.

"Today's ruling is a watershed win for good men and women all across America and is the result of a decades-long fight the NRA has led," NRA executive vice president Wayne LaPierre said in a statement.

"The right to self-defence and to defend your family and loved ones should not end at your home."

But New York Governor Kathy Hochul called the ruling a "dark day."

"It is outrageous that at a moment of national reckoning on gun violence, the Supreme Court has recklessly struck down a New York law that limits those who can carry concealed weapons," Hochul said.

Justice Clarence Thomas wrote the majority opinion and was joined by the other five conservatives on the court, three of whom were nominated by former president Donald Trump.

"Because the State of New York issues public-carry licenses only when an applicant demonstrates a special need for self-defence, we conclude that the State's licensing regime violates the Constitution," Thomas said.

"The Second and Fourteenth Amendments protect an individual's right to carry a handgun for self-defence outside the home."

Thomas said the New York law prevents "law-abiding citizens with ordinary self-defence needs from exercising their Second Amendment right to keep and bear arms in public for self-defence."

The ruling comes as the US Senate is considering a rare bipartisan bill that includes modest gun control measures.

A country of mass shootings

On May 14, an 18-year-old used an AR-15-type assault rifle to kill 10 African Americans at a supermarket in Buffalo, New York.

Less than two weeks later 19 children and two teachers were shot and killed at an elementary school in Uvalde, Texas, by another teen with the same type of high-powered, semi-automatic rifle.

The New York law said that to be given a permit to carry a firearm outside the home, a gun owner must clearly demonstrate that it is explicitly needed for self-defence.

Gun-rights advocates said that violated the Second Amendment of the Constitution, which says "the right of people to keep and bear arms shall not be infringed."

The three liberal justices on the court dissented from the ruling.

"Many states have tried to address some of the dangers of gun violence... by passing laws that limit, in various ways, who may purchase, carry, or use firearms of different kinds," Justice Stephen Breyer said.

"The Court today severely burdens states' efforts to do so."

More than half of US states already allow permitless carry of firearms, most of them only doing so in the past decade.

But more than 20 still maintain restrictions which they could now be forced to abandon based on the court's ruling.

The New York state law dated to 1913 and had stood based on the understanding that individual states had the right to regulate gun usage and ownership.

Over the past two decades more than 200 million guns have hit the US market, led by assault rifles and personal handguns, feeding a surge in murders, mass shootings and suicides.

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