According to a live stream video of the attack, the man, who is yet to be identified, could be overheard saying "Hello, brother" as the gunman approached the entrance of the Al Noor mosque in central Christchurch.
At least 49 people, including children, were killed in Friday's attacks targeting the Al Noor and Linwood mosques. Police said on Saturday morning that 42 people were being treated for wounds following the "terrorist" attack. Two of them, including a four-year-old child, were in critical condition.
Video footage of the assault, which has been widely shared on social media, showed a gunman shooting indiscriminately at worshippers as they ran for safety or lay huddled on the floor.
As the attack shocked New Zealand, a nation where violent crime is rare, several social media users hailed the Muslim man who greeted the attacker before he was murdered.
"'Hello, Brother' were the last words of the first New Zealand victim. As he faced a rifle, his last words were peaceful words of unconditional love. DO NOT tell me that nonviolence is weak or pacifism is cowardice," one Twitter user said.
"The first Muslim man to die, his final words were 'hello brother'. These words were uttered by a man who symbolised Islam. He had a rifle pointed at him by a man with clear intentions to kill and how did he respond? With anger? With aggression? No, with the most gentle and sincere greeting of 'hello brother'.
"Perhaps this hero was trying to defuse the situation? Maybe Allah used this man to show the world the kindness that is Islam. I don't know but what I want, is to make certain, is that this detail isn't lost amongst you. That this mans final act was an Islamic one, a sincere courageous and warm way to stop violence instead of fuelling it".
"'Hello brother' a word came out of a pure soul filled with a peaceful faith. 'Hello brother' was said to a killer with a rifle pointed to this greeting. 'Hello brother' he said thinking that he is talking to a human with soul and feelings. 'Hello brother' was shot dead," another wrote.
"Hello brother and the reply was three bullets - Bi-ayyi thanbin qutilat (For what crime. She was killed) [Quran: 81, v9]," said another.