Blackburn Rovers defender Nelsen, whose family still live in Christchurch, told reporters on Friday he had struggled to comprehend the scale of the destruction as he watched television footage of the disaster.
At least 113 people were confirmed dead and more than 200 were listed as missing on Friday, three days after the 6.3 magnitude quake wreaked carnage in the South Island city during a busy lunchtime.
All Whites captain Nelsen, 33, said he had been awoken in the early hours of Tuesday by a flurry of text messages from friends.
And in a dramatic turn of events, the footballer's sister, who was 37 weeks pregnant, went into early labour after the quake before giving birth to a baby boy, George.
"I put CNN on and just saw what was going on. I tried to call my parents but obviously phones were down and mobile phones weren't working," Nelsen said.
"It was about 6am or 7am when I finally got hold of my parents, which was a big relief when they said they were okay. But then they said my sister had been knocked down.
"She was 37 weeks pregnant and she's got brittle bone disease so that was really worrying. She had to get from her house to hospital and the place was in a state of emergency. It was an absolute wreck, all the roads were gone.
"My parents didn't know if she'd made it, then she had to go into surgery, so it was a really stressful morning. At training I had a phone by me and I was just waiting for some good news, and when it came it was a huge relief.
"From all the carnage and all the havoc it's a really nice glimmer of light to come out of it."
Blackburn have granted Nelsen permission to fly back to New Zealand on compassionate grounds although he intends to remain in England for the time being.
"If my family wanted me to go back, I'd go back tomorrow because it puts everything into perspective," he said.
"I grew up in Christchurch. I played in the parks, I ran around all the monuments. To see all your memories destroyed is surreal."
Nelsen, who will wear a black armband during Blackburn's meeting with Aston Villa on Saturday, said he hopes to help in the fundraising effort to rebuild Christchurch.
"Once the dust settles we'll figure out a plan of what I can do to help but the damage is so ridiculously high that the city will need a lot of help," he said. "We're talking in the tens of billions to regenerate the city again."
New Zealand skipper Nelsen stunned by quake
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