If they hadn't been running a few minutes late they could have been hit by the blast, he said.
"If my Australian friend Jason had been on time we would have been five minutes earlier going out the gate as the bomb went off. I'm a lucky boy,'' he said.
Mr Carter was waiting in the carpark of the secure compound when he witnessed the explosion, and felt the force of the bomb on his face.
''....Just in front of us a US convoy had just gone past our compound and it was attacked by a suicide bomber in a vehicle laden with explosives,'' he told Newstalk ZB.
"It destroyed one of the American vehicles, destroyed a civilian car that was just behind them, and if we'd been just five minutes earlier we would have been the ones behind them.
"They weren't aiming for the UN, they were aiming for the Americans, but we would have been hit by the bomb.''
Mr Carter said the whole experience had felt surreal, and seeing it unfold had felt like he was watching a movie.
"I guess that's a distinctive human way of coping with a very dramatic and dangerous situation like that,'' he said.
He said he was hit by a rush of air pressure from the blast.
"I had my face slightly turned to the explosion, so the right hand side of my head - particularly my ear - feels very blocked at the moment,'' he told Radio New Zealand.
Mr Carter said he and others affected by the bomb would be getting their ears examined by American specialists at a hospital tomorrow.
Six members of a local family driving past were killed and four US soldiers in the convoy were seriously injured, Radio NZ reported.
However, Mr Carter, who has worked in Afghanistan for two years in his role helping to build local government in the war-torn country, said he doesn't "dwell on the dangers of the job''.
