Connecticut's supreme court has ruled that US gunmaker Remington can be sued over the massacre at the Sandy Hook elementary school in which one of its weapons was used.

The attack, which took place just before Christmas 2012, left 20 school children and six members of staff dead.

The 4-3 ruling by the state court raised hopes among the victims' families of punishing the marketers of the powerful Bushmaster AR-15 assault rifle used by the shooter, Adam Lanza.

It also sets a precedent that could lead to more lawsuits against manufacturers whose guns are used in mass shootings.

The ruling on Thursday overturned a lower court's judgment rejecting the lawsuit, which charged that Remington Outdoor Co., arms distributor Camfour, and the Connecticut store which sold the gun used in the massacre could be held liable.

Lanza was a 20-year-old with known developmental disabilities who lived at home with his mother when he carried out the attack.

His mother, a gun enthusiast, had bought him the AR-15-style Bushmaster XM15-E2S semi-automatic rifle more than two years before the shooting. Lanza murdered his mother before assaulting the school, and killed himself afterward.

The lawsuit alleged that Remington and the other two defendants are culpable because they knowingly marketed a military grade weapon that is "grossly unsuited" for civilian use yet had become the gun most used in mass shootings.