Smoking is to be banned in NSW national parks, the state government has announced.

Environment Minister Rob Stokes said the ban would lessen the risk of bushfires and reduce litter.

Seven billion cigarette butts are dropped in Australia every year and as well as looking unsightly, they contain hazardous chemicals such as arsenic and lead, which can then leach into the environment.

Wildlife can also eat cigarette butts.

Making the announcement on Sunday, Mr Stokes said the ban would apply to picnic areas, campgrounds, beaches, lookouts, walking tracks and national parks roads.