US President Donald Trump has called to fast track the death penalty for "mentally ill monsters" who commit hate crimes and mass shootings but says guns aren’t to blame.

"Hate has no place in America": Trump's response to mass shootings

In a few weeks time, the US summer break will be over and parents will be sending their kids back to school.

But, as they shop for the usual supplies, such as pens, notebooks and crayons, they are likely to notice a product that, anywhere else in the world, looks alarming — bulletproof backpacks.

Several pictures have gone viral on social media this week showing a range of the mind-boggling bags in a range of colours on sale at US supermarkets.

“Saw this at Office Maxx today and my heart literally broke into pieces,” a stunned parent wrote alongside a picture of the bags, which cost around $US120 have a marketing tagline that bleakly reads: “Protection is in Session”.

RELATED: El Paso shooting victims named, gunman faces death penalty

RELATED: Ohio shooting: Nine dead, 27 injured after gunman opens fire

The post has now been shared hundreds of thousands of times, with parents around the world expressing shock and questioning whether the product was a joke.

Well, not only is the product real but it’s selling like hot cakes.

Guard Dog Security’s ProShield Scout backpacks are being stocked at a number of retailers across the US for up to $300 a pop — but many stores are struggling to keep up with demand.

Yasir Sheikh, president and founder of Skyline USA, the company that makes the Guard Dog bags, told MSNBC “we have sold out a few times this year” and sales spiked after the weekend that saw two mass shootings in the space of 24 hours.

Roman Zrazhevskiy of ReadyToGoSurvival.com told the Houston Chronicle that bulletproof backpack orders over the weekend were more than just unusually high.

“Our baseline is 100 units a month,” Mr Zrazhevskiy told the newspaper. “We sold 300 units just over the last few days.”

Another company, Bullet Blocker, which has been selling bulletproof backpacks for more than a decade, says its sales have skyrocketed by more than 200 per cent in recent years.

According to the product description on the Guard Dog website, the ProShield Scout backpack is “designed for student’s everyday carry”.

“The Guard Dog ProShield Scout looks like a regular backpack yet boasts LEVEL IIIA protection,” it reads. “With a laptop sleeve and organisational pockets, the Scout is just ounces more than a non-armoured backpack.”

Other manufacturers like ArmorMe go even further, asking parents to practice mass shooting scenarios at home with their kids — using a bulletproof bag as a shield.

“We never know when or where violent attacks may happen,” its website reads. “Designed for everyday use, our stylish, eco-friendly bags hide a solid wall of bullet-resistant material to provide instant protection from handgun attacks.”

However, gun-control advocates say there is no evidence that armoured backpacks, no matter carefully tested, would keep children safe during a shooting.

“We’re asking children to stand up to gunmen because politicians are too afraid to stand up to the gun lobby,” said Shannon Watts, the founder of a grassroots gun-control organisation told the New York Times. “There isn’t a parent in this country that isn’t terrified. These companies are capitalising on that.”

However, Gabi Siboni — who runs ArmorMe — said the criticism was unfair.

“Whatever you do, you’re capitalising on something,” he told the Times. “We are just responding to a need.”

The Guard Dog website also states the company will give a portion of every bulletproof backpack sale to national non-profit organisation dedicated to protecting students and teachers at school.