Democratic state lawmakers have a new target as they aim to tighten New Jersey's already strict firearms laws: "ghost guns."

A new bill that began advancing in the Democrat-controlled state Legislature on Monday would prohibit the purchase of firearm parts used to make these untraceable homemade guns.

The state Senate Law and Public Safety committee approved the measure along with a package of six other Democrat-sponsored gun-control bills that continue to move closer to Gov. Phil Murphy's desk.

The state Assembly already approved those six proposals last month -- which include reducing the number of rounds allowed in a magazine from 15 to 10 (S102), banning armor-piercing bullets (S2245), strictly defining that residents must show a "justifiable need" to obtain permit to carry a handgun (S2376), expanding background checks for private gun sales (S2374), and making it easier to seize weapons from people deemed to pose a threat to themselves or others (S160 and S2259).

But this was the first time members of the state Senate considered the bills. And it was the first time the "ghost gun" measure (S2465) was considered by any lawmakers.

State Sen. Joseph Cryan, a main sponsor of the bill, said such weapons are made when people purchase parts one piece at time and assembly them using a kit you can buy online. Thus, he said, the weapons have no serial or registration number.

Bryan said the process allows people prohibited from having a gun -- such as felons and those with mental illness -- to create their own firearm.

"This 'do it yourself' method of assembling these 'ghost guns' allows the owner to avoid the laws and regulations that are meant to keep firearms out of the hands of those who pose a danger to themselves or others," said Cryan, D-Union, a former Union County sheriff.

"Ghost guns" have drawn more attention since November, when a northern California man -- who was prohibited from having firearms because of a restraining order -- made his own semiautomatic weapon at home and killed his wife and four other people and wounded 12 others last month before being killed by police.

But Marcus Hirschorn, a gunsmith, told the Senate committee Monday that the New Jersey measure is too broad.

"If an overzealous prosecutor gets hold of this bill, technically any piece of steel big enough to turn into a gun could in theory wind someone up in jail," Hirschorn said.

It's already illegal in New Jersey to make a handgun, rifle, or shotgun without a license, and it's illegal to manufacture any machine gun, sawed-off shotgun, or assault rifle here.

But this measure would also ban the purchase of any combination of parts to assemble a firearm without a serial number.

Breaking the law would be a third-degree crime, and those that violate it would face three to five years in jail, a fine of up to $15,000, or both.

Democrats' push to strengthen New Jersey's gun laws -- already among the toughest in the U.S. -- comes amid a nationwide debate over firearms in the wake of the Parkland school shooting and a number of other massacres.

Murphy, a Democrat who took office in January, has pledged to sign the batch of new gun-control measures if they are passed by the full state Senate -- which is expected.

On Monday, the governor released a statement applauding the Senate committee for passing what he called "common-sense gun legislation" that will keep the state's "children and families safer."

"As gun violence continues to plague our country, New Jersey will lead the way by setting a higher standard for gun safety," Murphy added.

At the beginning of Monday's marathon hearing -- which lasted more than five hours -- Ethan Block, a 16-year-old high school sophomore from Hopewell, said he and his fellow students "have a genuine fear of being gunned down in the halls of our schools."

"If you are not able to get this done, then we will," Block added.

But gun-rights advocates say many of the measures are redundant, won't help make the state safer, and violate the Second Amendment of the U.S. Constitution.

Anthony Colandro, who owns a firearms range in Woodland Park, was one of many who said the state is simply hurting law-abiding citizens by pushing laws that criminals will ignore.

"We the people have had enough," Colandro said. "We are tired of you rich socialists running every aspect of our lives while we are required to shut up, work, and pay our taxes. I've had many of my customers and firearms owners tell me that this is the last straw and they will not comply."

It will now be at least nearly two months until the full Senate votes on the bills. The chamber's next session in June 7.

The "ghost gun" bill must also be approved by the state Assembly before it reaches Murphy.

Brent Johnson may be reached at bjohnson@njadvancemedia.com. Follow him on Twitter @johnsb01. Find NJ.com Politics on Facebook.