Vermont lawmakers have given final legislative approval to a bill that raises the legal age for buying firearms and expands background checks, becoming the latest state poised to tighten gun restrictions after last month's Florida school massacre.

The Vermont bill raises the age for gun purchases to 21 and expands background checks for private gun sales.

It also bans magazines of more than 10 rounds for long guns and 15 rounds for pistols as well as rapid-fire devices known as bump stocks.

The Democrat-controlled state Senate approved the measure in a 17-13 vote on Friday, according to the online legislative record after the bill passed the state House of Representatives this week.

The measure now goes to Republican Governor Phil Scott, who has shifted his stance and voiced support for some gun controls after the arrest in February of a Vermont teenager accused of threatening to shoot up a high school.

The incident came two days after a former student killed 17 people at Marjory Stoneman Douglas High School in Parkland, Florida, on February 14.

Scott's support for gun controls marked a sharp switch for a governor with a 93 per cent approval rating from the National Rifle Association (NRA) gun rights advocacy group in an otherwise politically liberal state with a reputation as a pro-gun stronghold.

Vermont, a largely rural New England state with a passion for hunting, is one of two dozen states where efforts to curb gun violence have gained momentum since the shooting at Marjory Stoneman Douglas High.

The shooting sparked demonstrations across the nation by thousands of students demanding that politicians do more to ensure their safety.