An American judge has blocked a Tennessee law that allowed people to bring handguns into restaurants and bars.

The law that took effect in July allowed handgun owners with permits to pack their pistols in places serving alcohol, providing the establishments made more than half their profits from food.

Nashville Judge Claudia Bonnyman said the law was "fraught with ambiguity" and ruled in favour of a suit brought by restaurant owners who argued gun owners would not be able to determine if an establishment met the criteria.