A dog that attacked a toddler at her home in Porirua, north of Wellington, on Saturday has been destroyed and no charges will be laid.

The 18-month-old girl was playing in her backyard when the family's pitbull-staffordshire-cross dog lunged at her, causing significant injuries to her face and stomach.

She underwent facial reconstruction surgery at Hutt Hospital and has since been discharged.

Acting Kapiti Mana Area Commander Detective Inspector Ross Grantham said the girl's family gave permission for their dog to be destroyed.

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"No charges will be laid in relation to this incident and no further police action will be taken,'' he said.

The attack was one of three in less than a week; a 9-year-old girl was left with deep cuts to her head and arm after being attacked by her neighbour's American bulldog in Rotorua on Sunday afternoon and a 3-year-old boy was left in a critical condition after an attack in Ashburton last Wednesday.

In the Rotorua attack, the owner of the dog said his partner had been walking with the dog on its lead and six children, including the victim.

The girl was bouncing a ball when the dog took to her arm and head.

The owner's partner tried to pull the dog away and threw herself over the girl to protect her from the dog.

The Ashburton boy remains in a critical but stable condition in Starship Hospital's intensive care unit after being bitten in the throat.

Local Government Minister Nick Smith said he was concerned about the recent spate of serious attacks and promised to begin a stalled inquiry into laws governing dangerous dogs. The investigation had been due to take place last year.