Dozens of graves were being dug in a Christchurch cemetery on Monday for the 50 worshippers killed in two mosque attacks, as families clamoured for the return of their dead.

People present floral tributes at a makeshift memorial for victims of the March 15 mosque attacks, in Christchurch on March 17, 2019. (Photo: AFP)

Coroners said they hoped to let grieving relatives fulfil Islamic burial customs soon, but insisted they had to move carefully through their investigation into the horrific multiple murder.

As New Zealand grappled to come to terms with the slaughter -- the worst attack on Muslims in a Western country in modern times -- tales of heroism, suffering and incredible grace emerged.

Farid Ahmad, whose 44-year-old wife Husna was killed as she rushed back into a mosque to rescue him, refused to harbour hatred toward the alleged gunman, Australian-born, self-avowed white nationalist, Brenton Tarrant.

"I would say to him 'I love him as a person'," Ahmad, who uses a wheelchair, told AFP. 

Asked if he forgave the 28-year-old suspect, who is being held in custody after appearing in court, he said: "Of course. The best thing is forgiveness, generosity, loving and caring, positivity." 

Husna Ahmad was among four women believed to have been killed by Tarrant, who documented his radicalisation and two years of preparations in a lengthy, meandering and conspiracy-filled far-right "manifesto".

Prime Minister Jacinda Ardern, who was holding a cabinet meeting Monday to address gun laws and intelligence failures, was among about 30 officials who received the document ahead of the attacks.

"It did not include a location, it did not include specific details," she said, adding that it was sent nine minutes before the rampage and handed to security services within two minutes.

Around Christchurch, New Zealand and the world there have been vigils, prayers, memorials and messages of solidarity.

An emotion-filled haka -- the Maori war dance -- was performed by a New Zealand biker gang to honour the Christchurch dead.

The country remained on high alert, with police on Sunday briefly closing an airport in the southern city of Dunedin -- where Tarrant had lived -- after an unidentified package was spotted on the airfield. The airport re-opened a few hours later.

In Australia, counter-terrorism police searched two homes early Monday, both near the town of Grafton where Tarrant grew up.

"The primary aim of the activity is to formally obtain material that may assist New Zealand police in their ongoing investigation," a police statement said.