When a lone gunman opened fire on a concert in Las Vegas, killing at least 58 and injuring more than 500, it marked the 273rd mass shooting in America in the last 275 days.

That same day, three people were killed in a shooting stemming from a “physical altercation” in downtown Lawrence, Kansas. The day before that, a 15-year-old boy was killed in a shooting in Memphis, Tennessee. Three others were injured.

The Gun Violence Archive – an independent, online database of gun violence incidents in the US – defines a mass shooting as a single incident in which four or more people are shot. According to their records, there have been 273 such incidents in the US in 2017 alone.

This may be an underestimate, however, as another database, Mass Shootings Tracker, lists the number as 338.

And the current year is not an outlier: There were 383 mass shootings in 2016, and 358 in 2015, according to the Archive.

Las Vegas shooting – in pictures Show all 15 1 /15 Las Vegas shooting – in pictures Las Vegas shooting – in pictures People scramble for shelter at the Route 91 Harvest country music festival after gun fire was heard Getty Las Vegas shooting – in pictures People carry a person at the Route 91 Harvest country music festival after shots were fired David Becker/Getty Las Vegas shooting – in pictures People run from the Route 91 Harvest country music festival after gun fire was heard David Becker/Getty Las Vegas shooting – in pictures A handout photo released via Twitter by Eiki Hrafnsson (@EirikurH) showing concertgoers running away from the scene (C) after shots range out at the Route 91 Harvest festival on Las Vegas Boulevard EPA/Eiki Hrafnsson Las Vegas shooting – in pictures People lie on the ground at the Route 91 Harvest country music festival after hearing gun fire Getty Las Vegas shooting – in pictures A man in a wheelchair is taken away from the Route 91 Harvest country music festival after hearing gun fire David Becker/Getty Las Vegas shooting – in pictures People stand on the street outside the Mandalay Bay hotel near the scene of the Route 91 Harvest festival on Las Vegas Boulevard EPA/Paul Buck Las Vegas shooting – in pictures FBI agents confer in front of the Tropicana hotel-casino after a mass shooting during a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Las Vegas police run by a banner on the fence at the Route 91 Harvest country music festival grounds after shots were fired David Becker/Getty Las Vegas shooting – in pictures An injured person is tended to in the intersection of Tropicana Ave. and Las Vegas Boulevard after a mass shooting at a country music festival Ethan Miller/Getty Las Vegas shooting – in pictures Metro Police officers pass by the front of the Tropicana hotel-casino after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures A woman sits on a curb at the scene of a shooting outside of a music festival along the Las Vegas Strip AP/John Locher Las Vegas shooting – in pictures A cowboy hat lays in the street after shots were fired near a country music festival in Las Vegas Getty Las Vegas shooting – in pictures Las Vegas Metro Police and medical workers stage in the intersection of Tropicana Avenue and Las Vegas Boulevard South after a mass shooting at a music festival on the Las Vegas Strip Reuters/Las Vegas Sun/Steve Marcus Las Vegas shooting – in pictures Sheriff Joe Lombardo (2-R) speaking during a press briefing in the aftermath of the active shooter incident on Las Vegas Boulevard EPA

These numbers far surpass any other developed country in the world, according to research out of the University of Alabama.

Hannah Shearer, a staff attorney for the Law Center to Prevent Gun Violence, says this is because gun violence in general is more prevalent in the US than any of these other countries.

“The reason is just that the type of weaponry that are most commonly used in mass shootings just aren't available in other countries,” Ms Shearer told The Independent. “...That’s what contributes to disproportionate rates of mass violence in the US.”

Eyewitnesses describe how they fled the Las Vegas shooting

Ms Shearer pointed specifically to the accessibility of semi-automatic weapons, or guns that can reload automatically, within the United States. Only seven states in the US currently ban such weapons.

Stephen Paddock, the man identified by police as the Las Vegas shooter, is said to have used automatic or semi-automatic guns in his attack. Police said he had as many as 10 weapons in his hotel room at the time.

Nevada law does not limit how many weapons an individual is permitted to buy.

FBI agents confer in front of the Tropicana hotel-casino on October 2, 2017, after a mass shooting during a music festival on the Las Vegas Strip in Las Vegas, Nevada (REUTERS/Las Vegas Sun/Steve Marcus)

The Las Vegas shooting has been named the deadliest in US history, surpassing last year’s record-breaking attack at an Orlando nightclub. That incident killed 49 people, and injured 58.

Ms Shearer said mass shootings have increased in both frequency and lethality in the last 10 years. It has been 13 years since the federal ban on semiautomatic weapons expired.

Gabrielle Giffords, a former congresswoman who was injured in a mass shooting in 2011, urged Congress take action on gun control on Monday.

“I am praying they find the courage it will take to make progress on the challenging issue of gun violence,” Ms Giffords said of her former colleagues.