California is declaring war on "ghost guns" -- weapons kits sold on the internet without any system of control -- with Los Angeles on Tuesday becoming the latest city to move to outlaw them.

City councilors in the metropolis -- the second largest in the United States -- voted unanimously to move to ban the sale or possession of the untraceable firearms whose use has exploded in recent years.

"When we see an increase in homicides here, and when we see that the (police) report that 40 percent of the crime guns recovered are ghost guns, we know that we have a very urgent critical situation that needs to be addressed," said Paul Koretz, the councilmember who proposed the ordinance.

Ghost guns first appeared around a decade ago, and became popular among weapons enthusiasts.

Also called "80-percent guns," they are sold as parts, and must be assembled by the end user.

Crucially, they have no serial number, and, because they are not classified as guns during the retail process, the kits do not require a license or a background check in many US states, including California.

Readily available online, they quickly became the go-to solution for people barred from buying a weapon because of a criminal record or their age.

The resulting proliferation is becoming a real problem for law enforcement, said Los Angeles Police Department Deputy Chief Kris Pitcher.

"Ghost guns have been around for approximately nine years, however, they have surfaced as a major problem in 2020 with the confiscation of 814 ghost guns just last year alone in Los Angeles," he said.

A study by Everytown for Gun Safety, an organization that fights gun violence, found that a kit to assemble an AR-15 rifle -- one of the most popular models in the United States, and often used in mass shootings -- can cost less than $400.

An online pitch for the weapon boasts how easy it is to assemble, according to the study.

"Building... doesn't take too long. Within an hour or two, you should be breaking it in at the range."

Anyone needing inspiration need look no further than YouTube, where tutorials with hundreds of thousands of views are not hard to find.

Legal loophole

The vote Tuesday brings Los Angeles closer to both San Diego and San Francisco in trying to rid the streets of the weapons.

The city of San Francisco is suing three manufacturers in a bid to staunch the flood of unlicensed guns.

"We directly take on those who are responsible for bringing these dangerous and unregulated weapons into the streets of San Francisco and throughout the state of California," said San Francisco District Attorney Chesa Boudin.

According to the Bureau of Alcohol, Tobacco, Firearms and Explosives, the government body that regulates gun sales on a federal level, two-thirds of the ghost guns seized in the United States last year were in California.

"California is sort of the epicenter" of this epidemic, says Adam Skaggs, legal director of Giffords Law Center, a non-profit named after Gabby Giffords, a former US representative who was seriously wounded in a 2011 shooting.

Ironically, California's tough gun laws -- which require stringent permitting and do not allow open carry -- are fueling the popularity of the 80-percent guns.

"Whether it's because of a criminal record, or a record of domestic violence, or if you're a minor... all of these people would be blocked from buying a gun at a gun store," he said.

"But they can get their hands on a ghost gun, because there is no background check."