Prime Minister Jacinda Ardern confirmed two of the 40 people being treated at Christchurch Hospital were in a critical condition - a five-year-old had also been taken to Starship Hospital at Auckland.
The court appearance lasted only about a minute, and he was led back out in handcuffs. One person died after being transported to Christchurch Hospital.
"It's outrageous, the feeling is outrageous", he said.
Prime Minister Jacinda Ardern designated the tragic incident a terrorist attack.
One Saudi citizen was killed and another wounded, according to Saudi-owned Al-Arabiya television news channel.
"Fortunately, the vast majority of New Zealanders never feel the threat of illegal firearms in their neighbourhood [sic]", then-assistant police commissioner Malcolm Burgess said in 2014.
She said she had been advised the gunman obtained a Category A licence in November 2017, and "under that, he was able to acquire the guns that he held".
The suspect documented his radicalization and two years of preparations in a lengthy, meandering and conspiracy filled far-right "manifesto".
It has been widely reported that the suspected gunman in the New Zealand massacre took to social media platforms to live stream his attacks.
Police say homes around a "location of interest" in Dunedin have been evacuated as a precaution.
Tributes to the victims poured in from around the world. But we utterly reject and condemn you.
Speaking in Sydney, Australian Prime Minister Scott Morrison described the gunman as "an extremist, right-wing, violent terrorist".
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Police did not immediately say whether the same person was responsible for both shootings.
He was not on a government watch list in either New Zealand or Australia.
The dead were said to include women and children.
Police later said one of the arrests didn't relate to the shootings. "Some were covered in blood", he told AFP.
Muath said his brother helped establish the mosque a year after arriving in New Zealand, where he teaches engineering at a university and runs a consultancy.
Just heard news of the devastating reports from New Zealand Christchurch. Friday is Islam's holy day.
Those new amendments included greater oversight over the acquisition of ammunition, restricting sales to only firearms license holders and requiring permits for people to order guns or ammunition by mail, updating and adding more information including photographs to individuals'gun licenses, and requiring secure storage for guns.
"Active shooter drills, situational awareness train our ushers and greeters about how to lock down the facility, where our evacuation routes are in the building", Orsini said.
"There were bodies all over", he said.
This is the worst mass shooting in New Zealand's history.
However, anyone over 16 can apply for a standard firearms license after doing a safety course and police check.
Meanwhile, the third cricket test between New Zealand and Bangladesh has been cancelled in the wake of the shooting.