''I am in shock. I'm just absolutely gutted. Everything is gone.''
Her son was inside when the fire broke out - she believed he was sleeping - but he escaped before fire crews arrived.
Nelson had prevented her girls (6 and 10) from leaving their new scooters outside in case they were stolen. Instead, they were destroyed by fire.
Oamaru Volunteer Fire Brigade station officer Mark Bradford said the fire was ''as bad as it gets''.
''When we got here, the whole house was just fully involved - it was just a wall of flame,'' he said.
''It was threatening two other properties with the wind and the close proximity of the houses. It actually got into a second property and we got a crew in and extinguished that before too much damage was done.''
Reed St between Exe and Nen Sts was closed to vehicles from about 2.45pm to 5.15pm as up to 30 firefighters mopped up hot spots.
Sergeant Tony Woodbridge, of Oamaru, said police were treating the fire as suspicious and asked anyone with information to contact them.
He said the 17-year-old youth was taken to Oamaru Hospital with serious injuries.
Fire and Emergency New Zealand fire-risk management officer Mark Bredenbeck said police believed they knew how the fire started.
He was called to ''make sure that cause fits with what happened at the scene''.
Due to the extent of the damage, it was not safe to go inside the house and he would conduct an ''exterior examination only''.
A man who lives across the street, who asked not to be named, said he heard two loud bangs, which could have been windows exploding, and went outside.
Before St John arrived, the 17-year-old boy was brought on to his property by a woman who "seemed to know what she was doing" and he was asked if he had a hose.
The boy sat in a chair and the woman turned the hose on him before the ambulance arrived. The man said the boy looked singed and yelled out.
The owner of the property, who visited the scene yesterday, declined to comment.
Bevan Smith, who lives next door, was not home when the fire started.
His tomato hothouse was destroyed and his gutters melted, but his house, "amazingly", was spared because the wind pushed the fire into the house behind his. The fire blew out the windows and caused extensive smoke damage to the second home.
Smith said he felt for Nelson and her children.
''Hopefully, Oamaru rallies around them,'' he said.