In the United States, suicidal behaviour has quietly morphed into a public health crisis, and it's one that's affecting some of the youngest people in the country.

For the second decade in a row, the number of children and teenagers visiting the emergency department for suicidal behaviour has almost doubled, and the median age is just 13 years old.

"The numbers are very alarming," paediatric emergency room physician Brett Burstein from McGill University told CNN.

"We are seeing an acceleration of this issue, and I worry that we have not yet seen the peak."

Using data collected by the Centres for Disease Control and Infection (CDC), the authors analysed over 30,000 visits to the emergency department for children ages five to 18.

In 2007, at the very beginning of the study, the authors tallied about 580,000 visits for suicide attempts or suicidal thoughts. By 2015, that number had skyrocketed to 1.12 million.

It's the second analysis in a row to show this alarming increase, and by the looks of things, the problem is only picking up steam. Using the same kinds of data, an earlier study reported a similar increase between 1993 and 2008.

That kind of replication has public health officials worried, and for good reason. Suicide is a major public health concern, and the second leading cause of death among youths age 10 to 18.

While it's true that suicidal thoughts among children are not always life-threatening, they are the most important indicators of future suicide attempts. In the nine years of the study, the authors noticed that visits to emergency department for suicide attempts increased by almost 80 percent.

Child psychologists have seen this coming for years, but that doesn't make the news any easier to swallow. Of all the hospital visits recorded for suicidal behaviour, nearly half were for young children aged five to 11.

From 1999 through to 2015, past CDC data has shown that 1,309 children between five and 12 took their own lives, roughly one every five days.

Lisa Horowitz, a paediatric psychologist at the National Institute of Mental Health, told USA Today that the statistics were stunning.

"It's just chilling," she said.

The exact reason or reasons for this trend remain unclear, making the crisis even harder to tackle.

"No conclusions can be drawn regarding the cause for the observed increase, which is likely multifactorial," the authors write in their report.

Nevertheless, past research indicates that children who die by suicide are more likely to have experienced mental health disorders and tense relationships with family and friends.

The problem is only made worse by a severe lack of child and adolescent psychiatrists, and the rise of cyber-bullying. 

"Findings suggest a critical need to augment community mental health resources, ED physician preparedness, and post-emergency department risk reduction initiatives to decrease the burden of suicide among children," the researchers conclude.

This study has been published in JAMA Pediatrics.

If this story has raised concerns or you need to talk to someone, here's a list where you may be able to find a crisis hotline in your country.