SUICIDE is now the most common cause of unexpected death among WA teenagers.

The revelation contained in a new report has already triggered a major investigation into youth suicide by the WA Ombudsman, The Sunday Times can reveal.

Eminent health experts say the fact that suicide now outranks car crashes and illness as the leading cause of sudden death among 13 to 17-year-olds was a cause for alarm.

Child death review data shows 39 per cent of youths from this age bracket who died suddenly between July 2009 and June 2013 took their own lives. This compares with 29 per cent from car crashes and 14 per cent from medical conditions.

"The Ombudsman (has) decided to undertake a major own-motion investigation into youth suicide," a spokeswoman for Ombudsman Chris Field said on Friday.

Responsibility for child death reviews was transferred to the WA Ombudsman in 2009. The state coroner is required by law to notify the Ombudsman of any unnatural, unexpected or violent deaths of children.

Of the 123 child death notifications for teenagers received by the Ombudsman since 2009, 48 involved children taking their own lives, including one child aged 13 and 18 children aged 14 or 15. Almost two-thirds were from the Perth metro area. One-third were Aboriginal.

Rosanna Capolingua, chair of the Governing Council for Child and Adolescent Health in WA, said she feared statistics for the second half of 2013 would be even worse.

"Something significant is happening to kids in that age group in WA and maybe across Australia for them to take their lives and we know that social media plays a big role in this," she said.

"I think parents are aware, doctors are aware, but sometimes we don't know what to do. As well as the bullying, social media encouraged children to dwell on negative emotions, such as pain and suffering. Suicide is heralded as a wonderful thing (on social media)."

She said early intervention was needed and we needed to "bust the myth" that talking about suicide would make the problem worse.

Australian Medical Association WA vice-president Michael Gannon said WA's mental health system was "collapsing."

"In the whole state we have got eight (mental health) beds available at PMH and another 12 beds available at Bentley and that's all we've got for adolescent patients," he said.

"Not only is there a reasonable amount of evidence that life just gets more stressful as every generation goes on and more difficult, these are also young people who unfortunately are increasingly exposed to illegal drugs which are extremely powerful in their effect on the brain and there is a higher rate of mental illness in people who are using illicit drugs."

Mental Health Minister Helen Morton said the causes were complex.

"We are working to ensure young people can access a dedicated youth-friendly stream of care and not fall in the gap between child and adolescent services and the adult system," she said.

Opposition Health Spokesman Roger Cook said he was "alarmed" by the figures, while Lifeline WA chief executive Fiona Kalaf said "families were often unsure about how to navigate the maze of mental health services."

Lifeline 13 11 14 (24-hour telephone service) crisischat.lifelinewa.org.au (online chat service)

Kids Help Line 1800 55 1800 (24-hour telephone service) www.kidshelp.com.au