Parents wait for news after a reports of a shooting at Marjory Stoneman Douglas High School in Parkland, Florida - FR170673 AP

Bill Bratton, the former New York police chief, has called it the "new normal".

The deadly gun rampage at a Florida high school on Wednesday took to 18 the number of school shootings across the United States so far this year - an average of one school shooting every 60 hours.

Mr Bratton said the statistic was "astonishing", but admitted that it was "the new normal".

"The reality is, this is something that will just continue to occur," he told MSNBC.

The stunning number underscored how commonplace gun violence has become in America, with students in primary and high schools regularly performing drills on how to react in an "active shooter" situation.

According to the independent Everytown for Gun Safety group, eight of the 18 school shooting incidents so far this year, which cover primary schools to universities, involved guns being discharged with no one injured.

Timeline | US school shootings in 2018

Two were suicide attempts, and the rest attacks on others.

The attack on Wednesday at the Marjory Stoneman Douglas High School in Parkland, Florida - about 50 miles north of Miami - appeared to be the worst so far in 2018, with at least 17 confirmed dead.

It also ranked as the third deadliest mass shooting at a school in modern history, after the Virginia Tech and Sandy Hook massacres.

Donald Trump offered his "prayers and condolences to the families of the victims" in the latest tragedy.

My prayers and condolences to the families of the victims of the terrible Florida shooting. No child, teacher or anyone else should ever feel unsafe in an American school. — Donald J. Trump (@realDonaldTrump) February 14, 2018

Democratic Congressman Ted Deutch of Florida thanked colleagues for reaching out to him, calling it both "heartwarming and obscene."

The congressman said he uses the word "obscene" because school shootings had become so commonplace that lawmakers were offering him guidance on what to expect in coming days as constituents grapple with the tragedy.

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Mr Deutch was among a number of politicians who urged the president "do something" about gun violence.

Former Congresswoman Gabrielle Giffords, the Arizona Democrat who survived being shot in the head in 2011, said the latest atrocity should "strike fear into all Americans".

Even in our grief, we must summon the courage to fight against this fear. We must find the courage to imagine a country where these massacres do not occur. Our leaders must find the courage to escape the confines of their politics & pursue the moral necessity of peace & safety. — Gabrielle Giffords (@GabbyGiffords) February 15, 2018

Saying it was the latest attack in an epidemic of gun violence that continues "days after deadly day", Ms Giffords said the tragedy should stir fresh resolve in Congress to "find the courage to pass the laws we need to protect our children".

I agree with every word @realDonaldTrump said here. I invite him to get off his ass and join me in trying to do something about it. https://t.co/XV0hRENr4B — Seth Moulton (@sethmoulton) February 14, 2018

Republicans should pray for forgiveness, for not only their complacency and dereliction of duty, but in contrition for the men, women and children we continue to lay to rest because of senseless gun violence and the cowardly inaction from Congress. — Bonnie WatsonColeman (@RepBonnie) February 14, 2018

A number of celebrities also called for action on gun control, with actress Bette Midler calling members of Congress "spineless cowards".

No words, no actions, no laws are enough until we end this epidemic of school shootings in our country. My heart is with the students and parents of Marjory Stoneman Douglas High School. — Ellen DeGeneres (@TheEllenShow) February 14, 2018

Yeah, someone is mentally ill: what a crock! IT’S THE GUNS STUPID!!! We are a nation in disgrace in the eyes of the world. I am so ashamed. — Bette Midler (@BetteMidler) February 15, 2018

The tragedy was too much for former CIA and FBI analyst Philip Mudd, who broke down in tears as he discussed the atrocity on CNN.

"A child of God is dead," he said. "Can we not acknowledge in this country that we can't, we cannot accept this?"

Ending the interview abruptly, he said: "I can't do it ... I'm so sorry. We can't do it."

CNN contributor Philip Mudd breaks down in tears discussing the Florida shooting pic.twitter.com/oKCMgMWxDP — David Mack (@davidmackau) February 14, 2018

However, Republican Florida Senator Marco Rubio responded to calls for greater gun control by saying a law might not have prevented the shooting.

He said "people still don't know how" the shooting occurred, or how the suspect Nikolas Cruz obtained the weapon.

"I think it's important to know all of that before you jump to conclusions that there was some law that we could have passed that would have prevented it," Mr Rubio said on Fox News.

He also said it was too early for his Senate colleagues to call for new laws.

In brief | Worst US mass shootings

"I think you can always have that debate," Mr Rubio said. "But if you're gonna have that debate about this particular incident you should know the facts of that incident before you run out and prescribe some law that you claim could have prevented it."

Florida Governor Rick Scott - who described the massacre as "just pure evil" - declined to make a statement on gun control in the aftermath of the shooting.

"There's a time to continue to have these conversations about how through law enforcement, how through mental illness funding that we make sure people are safe, and we'll continue to do that," said Mr Scott, a Republican.

Each incident like the one in Parkland brings calls for more strict laws on gun sales and ownership, but gun rights campaigners regularly succeed in stifling those calls.

Indeed, laws on carrying guns in public have been made less strict in many areas.

The thing we once called unthinkable has happened nearly 300 times since Sandy Hook. https://t.co/M0s4bqF53G



An early look at Thursday's front... pic.twitter.com/tZ6sjZC9cy



— New York Daily News (@NYDailyNews) February 15, 2018

"This is US," the New York Daily News declared on Thursday's front page, highlighting the fact there have been 300 such incidents in schools since the Sandy Hook tragedy in 2012.

In those six years, there have been 1,607 mass shootings, with at least 1,846 people killed, according to the Gun Violence Archive.

A look at Thursday's paper: 17 killed in "catastrophic" school shooting in Florida; Historically black colleges weather struggles pic.twitter.com/cC6DjiFnHK — USA TODAY (@USATODAY) February 15, 2018

When it comes to major mass shootings (where more than four people are killed), there have been an average of just 72 days between events during the period of 2010 to 2017 .

More than a person a day have been killed in US mass shootings in recent years

This is a far more frequent rate when compared to the average gap of 162 days from 2000 to 2010, according to data compiled by Mother Jones.

Florida in particular has been the setting of several particularly deadly shootings in recent years.

The worst remains an attack on an Orlando gay nightclub on June 12, 2016, which saw a heavily armed man - who pledged allegiance to the Islamic State group - kill 49 people.

Six months later, a man opened fire at Fort Lauderdale International Airport, killing five people on January 6, 2017.

The state, home to 21 million people, has handed out more gun permits than any other state - around 1.9 million as of January, according to official statistics.

But this only makes up part of the total number of firearms, an unknown figure that cannot be estimated.