The response to the Christchurch terror attacks shows that humanity will overcome the world's "vicious cycle of extremism", Prime Minister Jacinda Ardern told thousands at National Remembrance Service in the grieving city today.

Around 25,000 Cantabrians packed into North Hagley Park this morning – just a few hundred metres from Al Noor Mosque where a gunman slaughtered Muslim worshippers a fortnight ago – along with families of the 50 victims of New Zealand's worst ever terror attack.

Ardern, praised globally for her compassionate and strong leadership after the March 15 massacre, said that while New Zealand has never been immune to the "viruses of hate, of fear, of other", it can be a nation that "discovers the cure".

"We each hold the power, in our words and in our actions, in our daily acts of kindness. Let that be the legacy of the 15th of March," she said.

"The answer lies in our humanity."

British singer and prominent Muslim, Yusuf Islam, previously known as Cat Stevens, played classic peace ballad Peace Train and Don't Be Shy.

Stevens, who converted to Islam in 1977, told those "shining souls whose lives were snatched away in that moment of madness may peace be upon them".

"Peace in this world may take a bit longer," he said.

"We learn about things through their opposites and it's opposites like this – the evilness of that act and what drove it – we find its opposite - which is the love and kindness and unity which has sprung up right here in New Zealand."

Al Noor Mosque terror attack survivor, Farid Ahmed, whose wife Husna rescued children from the gunman before being killed returning to find him, said he forgives the murderer.

"I do not hate him, I cannot hate anyone," he said, adding he does not want a heart "boiling like a volcano, which has anger, fury and rage".

"I don't want a heart like this, and I believe no one does. If our heart is full of love then peace will start from here."

A powerful Islamic invocation, or Du'a, was delivered by Linwood Mosque Imam Lateef Alabi, who survived the terror attack that ended with seven of his worshippers dead.

"Peace be upon everyone. Kia ora," he said.

The Du'a drifted across North Hagley Park while the police helicopter hovered in the distance and armed police patrolled the crows and park perimeter.

President of the Muslim Association of Canterbury Shaggaf Khan also said that out of a "terrible act of darkness" has come light.

The best weapons against the "senseless and vile politics of hate" are to be found within each and every one of us, said Governor-General of New Zealand Dame Patsy Reddy.

History reminds us what happens when good people stand by and let evil flourish, she said.

"We are at such a point in our history," Reddy said.

"New Zealand faces a renewed moral challenge … With tolerance, kindness, respect, and understanding we can and will defeat poisonous malice that seeks to divide us. But only if we also have the courage to acknowledge and to call out discrimination and racism whenever we see it."

In a touching unplanned moment, two children whose father died in the shootings asked to say a few words.

"He was a really nice man," one little girl said.