Friday is the busiest day of the week for mosques around the world, when Muslims convene for Friday prayers. Wahabzadah told CNN he ran outside as soon as he heard the shots, grabbing a credit card reader along the way. He confronted a man in "army clothes" armed with guns and a camera.
To distract the shooter from the mosque, Wahabzadah said he threw the credit card reader.
"I just wanted to scare him so he doesn't come inside," he said. Unfortunately the shooter did make it in.
The credit card reader hit the shooter, who then ran back to the parking lot and began firing at Wahabzadah. The shooter dropped the first gun -- which Wahabzadah described as a shotgun -- and started shooting with the second. The gunman couldn't get a good angle on Wahabzadah, he said, because Wahabzadah was ducking between cars and a fence.
Thinking the shooter was going to a car to get more weapons, Wahabzadah said he picked up the dropped gun, ran after the man and tried to pull the trigger, but realized the gun was empty.
"When he sees me ... chasing with a gun, he sat in his car," Wahabzadah said. "And I just got the gun and throw it on his window like an arrow and blast his window. And he thought probably I shot him or something and ... he drove off."
Wahabzadah didn't stop there. He said he continued chasing the shooter, who did a U-turn and raced off. It was then that Wahabzadah says he returned to the mosque to discover the scope of the violence.
Latef Alabi, the imam at Linwood, told the Australian Broadcasting Corporation that were it not for Wahabzadah's actions, the death toll would have been higher.
"I promise you I wasn't frightened or anything," Wahabzadah said, adding that he was prepared to give his life for those he loved. "I was doing my job. If anyone was there in that situation (they) would do the same thing as I did."
Wahabzadah said people at the mosque praised him for his actions.
"I got to be honest with you, it wasn't me, it was God that saved everybody. God saved everyone," he said.
Originally from Afghanistan, Wahabzadah said has been living in New Zealand for more than 2 years. Prior to the move, he said he was living in Australia for 27 years as a refugee.
Wahabzadah said that after seeing racism in Australia, he moved to New Zealand because it was a peaceful country.
CNN's Amir Vera and Jennifer Deaton wrote and reported from Atlanta, and Matthew McKew reported from Christchurch.