Olympic medallist and past Boston Marathon winner Lorraine Moller broke down as she watched the horrifying scenes unfold at a finish line she knows well.
Ms Moller, who won the race in 1984, is originally from Putaruru but now lives in Colorado with her husband and daughter.
She had planned to go to this year's event to help organisers - something she had done for the past few years - but with her husband away decided to stay home with 12-year-old daughter Jasmine.
"I thought to miss it this year and go next year and I'm glad I did.
"A friend called and told me. I turned on the the television and it was shocking. I shed tears about it today. I couldn't believe it."
She ran the course again in 1992, where she was the masters winner at the Boston Marathon.
That same year she represented New Zealand at the Barcelona Olympics, where she picked up a Bronze Medal.
Following news of the bomb explosions, Ms Moller spent the next few hours frantically trying to get in touch with friends who had participated - including one whose husband she had organised to be seated at the finish line.
"I heard from them and they had found that the bleacher that he was assigned to sit in had an unexploded bomb under it. It was one of the ones that didn't go off.
"He's fine. His wife came in and they left. She came in right before the bombs went off."
Ms Moller said she had got to know race organisers very well over the years and had often helped out at the finish.
"I know the finish line well. It's very crowded down. Because it's flagged from tall buildings, I can't imagine there's even a place to escape to [because] it's very tight."
Former marathon competitor Kathrine Switzer, the first woman to run in the Boston Marathon in 1967, was at yesterday's marathon with Kiwi husband Roger Robinson.
In a message on Facebook, she told friends and family: "A horrible explosion has just occurred at the finish line of the Boston Marathon. Many of you know that I was on the photo bridge doing TV of the race. I had left the area just before the explosion and am now in my hotel with my husband.
"This is a sad, sad day. Please hold everyone here in your thoughts and prayers."
The Edge radio host Dominic Harvey is also a former competitor and travelled with wife Jay-Jay Feeney to compete in 2011.
Waking up to the news yesterday morning, he said it was hard to watch the footage.
"I was completely shocked. It seems to hit home so much more when you have experienced the Boston Marathon first-hand.
Harvey, who trained for two years before he qualified to run in the marathon, said one of the big things he remembers were the spectators.
"The city embraces this marathon unlike any other run in the world, so the spectator areas from mile one to 26 are full of people who cheer on runners they don't know from a bar of soap. The thought of these people being hurt is horrendous."
Feeney said she was feeling disturbed by the events, knowing she had once sat near where dozens of dozens of people had been hurt.
"I was sitting in those stands at the finish line as Dom came over. The area where the bombs hit was crammed with people. We stayed at the Lenox Hotel, which was evacuated, and that's right beside the finish line. It's just so horrible to think it could happen."
Ms Moller said she hoped the bombing would not put people off marathons, but acknowledged that the tragedy would have a huge impact on future races.
"There's a lot of heart there at the finish. To have somebody just come and blow it apart, it's just tragic. It's just a mean-spirited act."