Farid Ahmed, whose wife Husna Ahmed was one of 50 people killed in the March 15 attack on two mosques, addressed a crowd of thousands at a National Remembrance Service at Hagley Park.

Delegates from nearly 60 countries also heard Ahmed describe how he doesn't want hatred to be the prevailing emotion.

"I have chosen peace, I have chosen love, and I have forgiven," said Ahmed, who was wounded in the attack.

"I do not hate (the accused) - I cannot hate him, I cannot hate anyone."

Australian Brenton Tarrant is the alleged gunman who is charged with murder and is expected to face a raft of further charges next week.

The swelling crowd listened solemnly when the names of all 50 victims were were read out.

New Zealand Prime Minister Jacinda Ardern said a positive to emerge from "our darkest hours" was what she believes is a newfound respect and compassion towards the Muslim community.

"We may have left flowers, performed the haka, sung songs or simply embraced but even when we had no words, we still heard yours. And they have left us humbled and united," she said.

"Violence and extremism in all its forms is not welcome here. Over the last two weeks, you have shown that in your actions."

Australian Prime Minister Scott Morrison was in attendance, along with opposition leader Bill Shorten and Governor-General Sir Peter Cosgrove.

Before the service, the trio and their wives laid flowers at the adjacent Al Noor Mosque, the scene of one of the attacks.

Heavily armed officers patrolled the central city park, with snipers and elite staff from Australia reportedly boosting police numbers in what has been described as the country's biggest security operation.

Musician Yusuf Islam, formerly known as Cat Stevens, performed his songs "Peace Train" and "Don't be shy" after wishing peace for those killed and their affected families.

The ceremony coincides with remembrance gatherings around New Zealand which are taking coverage of the Christchurch event via big screens.

Thousands more were expected to attend a service at Auckland's Eden Park on Friday afternoon.