Smith escaped through the back of the mosque and ran to his car.
When someone said the gunman was coming out, he escaped over a wall and found a young woman lying in the road beside the mosque.
"I take my jersey off and I put it over this girl," he told the BBC.
"I didn't know her name and I don't know where she's from at the time. I'm just holding her, I don't know why but I'm stroking her back - she's already dead."
He told the BBC he spent hours at a community centre in the hope of finding her husband.
"I was just hoping to catch a glimpse of her husband. I need to find him. I don't know his name. I just need to know he's okay.
Friends who he had come to think of as "second family" were also killed, he said.
He said he feels "proud" of how New Zealanders have responded.
"People here have been good . They've looked after us," he said.