A mental health helpline has been inundated with calls following the massacre at two mosques in Christchurch.

"It's had five times the usual volume of calls," a Canterbury District Health Board spokeswoman said.

In the wake of the shootings, the DHB has highlighted the national mental health and addictions phone counselling service, which can be reached by calling or texting 1737.

"The events ... in Christchurch are distressing," the DHB said. "If you or someone you know needs mental wellbeing support or advice, then call or text 1737 anytime day or night to talk to a trained counsellor."

The "Need to talk, 1737" service, staffed by paid counsellors 24 hours a day 7 days a week, is part of the National Telehealth Service.

The Parenting Place in Christchurch has provided advice about how to talk with children about trauma.

"They need to understand the situation or news in terms of what it means to them and their own safety and well-being," according to an article the Parenting Place has published on its website.

The article says to let children know that what they are feeling makes sense.

Don't say "Oh, don't worry". Instead: "Let them know that you get their feelings by reflecting back to them …"

Tributes left with flowers at the Mt Roskill mosque after the Christchurch mosque killings. Photo / Jason Oxenham

Help them to put it in context and ask directly what it is they're worried about, the article says. Let them see your compassion, empathy and resilience. Know that it is okay not to have the answers they are asking for. And remind them of the goodness in the world.

Canterbury counsellor Christine Macfarlane has said parents should talk to their children about what happened, but shield them from traumatising images on TV and the internet.

"Immediately after any trauma, particularly for children, there is a need for adults to reassure them, to validate their feelings, to say they are there for them to support and look after them," she said.

"The other point is, if it's children who were in there witnessing it, to not have the TV on replaying the scary stuff, so they are not being exposed to traumatic events unnecessarily. That is the internet and TV.

"Of course if it's teenagers they will see it themselves on their own devices. But if it's little kids, they don't need to see that."

Need to talk? Free call or text 1737 any time for support from a trained counsellor.

Or if you need to talk to someone else:

Lifeline – 0800 543 354
Suicide Crisis Helpline – 0508 828 865 (0508 TAUTOKO)
Youthline – 0800 376 633 or free text 234
Kidsline – 0800 54 37 54 (for under 18s)
What's Up – 0800 942 8787 (for 5–18 year olds 1pm–10pm weekdays and 3pm–10pm weekends)
Depression Helpline – 0800 111 757 or free text 4202
Samaritans – 0800 726 666
OUTLine NZ – 0800 688 5463
Healthline – 0800 611 116