Malvern woman Jenny Szymanski said the teenage boy was screaming "I want to die, I want to die" on the far end of a station platform on Tuesday afternoon. She said three boys on the opposite platform were taunting and laughing at him.

Ms Szymanski said a man with a young child asked her to help, but that about 40 other people at the station south-east of Melbourne failed to act. Ms Szymanski, a former nurse, approached the teenager, fearing he was about to jump in front of the next train.

"I was looking at the clock and thinking the train is going to arrive in two minutes," she said. "My gut feeling was that if no one did anything he was going to jump. I walked up really slowly and said, 'it sounds like you are having a bad day'. He said, 'Yeah, I just want to die, I just want to jump.'"

Metro staff saw the situation unfolding and called station control to stop the train as it approached the platform. Staff also called police and gave assistance on the platform. The teenager was later taken to The Alfred hospital.

Ms Szymanski said Metro staff and police acted quickly but that she was horrified by the lack of response from fellow commuters.

"What floored me was that there would have been 40-plus people [on the platforms] - adults, professionals, all watching him yelling and watching all the heckling - and no one tried to stop what was going on," she said.

"It was like a sideshow. This kid was in a traumatic state and wanted to kill himself and everyone was watching this happen. He was being heckled by the other kids and everyone was just standing there looking. Where do we get off potentially letting that happen? Why didn't the adults there walk up and intervene?"

Beyondblue chairman Jeff Kennett said there was no rulebook for how to respond in these confronting situations. "I would have thought that one of those adults, before the woman intervened, might have tried to start a conversation with this man. And you could have had done that from a distance. But I'm very loath to say that there is a template that we all should follow because every circumstance is different."

Mr Kennett said people should always exercise caution when approaching someone under difficult circumstances. "We've heard so much recently about people who have taken ice and then become very violent, and a lot of people are cautious about going forward into situations that are confronting."

Metro spokeswoman Larisa Tait praised Ms Szymanski and the station's staff for their courage and quick thinking. She encouraged passengers who were concerned about other people's behaviour to alert staff or press the red emergency button located on every platform and train.

"Sadly, we regularly see incidents on the network where people are threatening self-harm or contemplating suicide, and they often have a traumatic effect on our drivers, staff and any customers who witness them," she said. "We provide our staff with a guidance framework on how to identify at-risk behaviours, and they always do the best they can in this type of situation."

What to do if you suspect someone is suicidal

·        Act promptly if you think someone is considering suicide. Without endangering yourself, approach them to let them know you care and want to help

·        Make sure you do not put yourself in any danger. Call triple-0 if they have a weapon or if you don't feel able to approach them

·        Ask the person if they are having thoughts of suicide

·        Do not dismiss the person's thoughts as "attention seeking" or a "cry for help"

·        Once you have established a suicide risk is present, take action to keep the person safe. A person who is suicidal should not be left on their own

·        Ask them how they are feeling and reassure them that you want to hear what they say. Express empathy

·        Encourage the person to talk to a GP about a referral to mental health services, or if they go to hospital, talk to psychiatric staff in the emergency room

List compiled by Mental Health First Aid Australia

For help or information call:

Lifeline 131 114

Beyondblue 1300 224 636

Kids Helpline 1800 551 800