Trauma experts are urging people to seek help if they feel distressed by the events and aftermath of the Sydney siege.

Australian College of Trauma Treatment director Michael Burge said for those directly involved with the siege, it was important not to underplay the trauma of the event.

"You can't underestimate the impact of the shock an event like this can cause," Mr Burge said.

"It comes out of the blue and can feel like it is destroying your way of life.

He said the brain found it difficult to process trauma as it was so out of the ordinary.

"The brain almost shuts down the reality of what is unfolding," he said.

"Our survival mechanism kicks in.

"It takes quite a while for the shock to settle."

Even people watching events like the Sydney siege unfolding on TV could be severely stressed, he said.

"Ambulance workers, journalists, police and those who are there helping victims can find a situation like this very difficult," Mr Burge said.

People can go through a process called disassociation, where people push down their feelings of distress.

"They push the feelings aside and that coping mechanism can lead to chronic emotional distress down the track," he said.

Stress now, severe symptoms later for some

Research shows that while many people would be feeling stressed now by the Sydney siege, for most, the traumatic feelings would not last and they would feel better after a short time.

But Mr Burge said for others who were more vulnerable, it could cause long-term anxiety and post-traumatic stress symptoms.

Where to seek support If you are feeling concerned, contact LifeLine on 13 11 24

If you are feeling concerned, contact LifeLine on 13 11 24 Kids Helpline: If you need to speak to a counsellor, call 1800 55 1800, 24 hours a day

Kids Helpline: If you need to speak to a counsellor, call 1800 55 1800, 24 hours a day In NSW you can contact your local mental health service via the NSW Mental Health Line on 1800 011 511

In NSW you can contact your local mental health service via the NSW Mental Health Line on 1800 011 511 Victims Services: You can call 1800 633 063, or visit their website here

His advice is that for some people, they need to keep across events to feel secure.

"But some others can become obsessed by it, particularly with 24 hour news coverage and social media coverage. They become a 'trauma junkie'," he said.

It is normal for people's mood to change when an event such as the Sydney siege happens, but if symptoms go on, people have been urged to talk to a professional.

Mr Burge looked after many of the people who were traumatised by Black Saturday bushfires.

"If your changed moods go on, then it's important to talk to someone," he said.

A counsellor or a good listener is ideal, as long as they are not judgemental, he said.

Experts said for parents of young children, it was best to limit the amount of exposure they had to the coverage.

Technology had 'significant impact' on victims

NSW Acting Commissioner of Victims Rights Mahashini Krishna said modern technology had a significant impact on these sorts of crises.

Sorry, this video has expired Mental Health Commissioner warns of future trauma from Sydney siege ( Michael Rowland )

"Nothing is confidential – everything has played out on social media or media, so it can have not only more of an impact on victims that are inside, but also people outside – the public at large are seeing more and being impacted more by this," Ms Krishna said.

"It could have an impact on peoples' sense of security in that they feel unsafe about what's happening, it may result in fear and shock as a result of what's happened as well."

Ms Krishna said services had also improved in the last 10 years.

"We have staff in here who are trained in trauma responses and they can provide crisis assistance to victims of the siege last night, but also to the public generally if they just want assistance on how to cope and deal with what happened," she said.

"We also have a counselling service that it is available.

"It has qualified counsellors who are social workers, psychologists or psychiatrists and they can provide counselling."