With 49 people killed in the mosque attacks, it was by far the deadliest shooting in modern New Zealand history.
Muzzammil Pathan arrived to offer his condolences for a friend, Imran Khan, who was killed at a second mosque in the suburb of Linwood.
Brenton Harris Tarrant, 28, appeared in court Saturday charged with one count of murder.
Tarrant left the gym in 2011 and his travels, he says, were funded by money he made investing in Bitconnect - an open source cryptocurrency that collapsed in early 2018 amid charges it was a glorified Ponzi scheme.
Handcuffed and wearing a white prison suit, Tarrant did not speak.
At the nearby hospital, doctors worked round the clock to treat 39 people for gunshot wounds and other injuries sustained in the attacks.
Ardern said New Zealand has suffered an "extraordinary and unprecedented act of violence", lamenting in particular that the violence targeted the country's immigrant population.
"At this tragic time, my thoughts and prayers are with all New Zealanders", she said in her message.
The killing rampage touched a nerve around the world. Much love @ New Zealand", New Zealand's former captain Brendon McCullum tweeted."So sad to hear of the #NewZealandMosqueAttack In #Christchurch.
"We have seen what happens in the United States when gun radicals are involved".
Video of the shooting begins with the gunman driving to the mosque clad in tactical gear, his auto full of weapons. Reuters was unable to confirm the footage's authenticity and police urged people not to view or share it.
Imran had dropped off his father, an electrical engineer, at the Al Noor mosque on Friday and was looking for a parking space when the shooting began.
Thirty-six minutes after the police received the first call, Tarrant was in custody.
A number of patients are expected to be discharged from the Christchurch Hospital's Intensive Care Unit to surgical wards on Sunday, with plans to prioritise, "those patients from the mosque attack for surgery over the coming days". "We're also removing any praise or support for the crime and the shooter or shooters as soon as we're aware".
Leaders around the world expressed sorrow and disgust at the attacks, with some deploring the demonization of Muslims. Two others two remain in custody in connection with the shooting, but their role remains unclear.
In his manifesto, he wrote in all capital letters: "Why won't somebody do something?"
However, the weapons were not legal as they were found by the police after the attack.
"He was a good old man".
The two-year-old boy was reported to be in stable condition, as was the 13-year-old.
She has been airlifted to Starship children's hospital in Auckland, the country's top paediatric centre.
Underlining that the "time has come for change", Jacinda Ardern said that five guns were used by the perpetrator, including two semi-automatic weapons, and two shotguns.
Authorities were working to find out how he had obtained the weapons and a license, and how he was able to enter the country to carry out the attack, she said.
"I can tell you right now our gun laws will change", she said. It was the latest sign that a lethal vision of white nationalism has spread internationally.
He was recently based in Dunedin, a city about 225 miles to the south of Christchurch, she said.
Police said they had released a preliminary list of the victims to families, which has helped give closure to some who were waiting for any news.