A 17-month-old baby has been mauled to death by a dog as her family attended a party downstairs unaware.

Marley Wilander had gone to a Fourth of July party in Illinois, US, with her parents when the horror incident happened.

The bub had been placed in a playpen in an upstairs bedroom at their friend's house while two pit bull mixes were in the basement.

After hearing a commotion upstairs about 1.30am, the homeowner went to check it out and discovered one of the dogs biting the little girl, local media reports.

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The homeowner separated the dog from the child, who had "bite marks throughout her body", and called emergency services, police said.

Marley was rushed to hospital but later died. Preliminary autopsy results show she died from the dog attack.

It is not clear how the dogs escaped from the basement undetected by the adults at the party.

Marley Wilander with her parents. Photo / GoFundMe
Marley Wilander with her parents. Photo / GoFundMe

A neighbour who was watching the fireworks nearby described the party as "raging until nearly midnight", the NY Post reports, adding the suburb was known for having dogs running around unattended.

No charges had been filed in the incident but the dog had been turned over to local animal control.

A GoFundMe page has been set up by two "lifelong friends" of Marley's parents Daniel Wilander and Chelsea Cirino to help pay for funeral costs and medical bills.

"Marley was not only the whole world and universe of her parents, but a sign that hope, love, innocence and purity was always more powerful than the negative," the page states.

"We are attempting to accept donations of any kind in hopes to make this time of need as easy as possible for a grieving family recovering from a terrible tragedy."

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Currently the fundraiser has donations of more than US$30,000 ($A45,784) and has been flooded with messages of condolence.

Marley was upstairs in a playpen at her parents' friend's house when the two dogs escaped. Photo / GoFundMe
Marley was upstairs in a playpen at her parents' friend's house when the two dogs escaped. Photo / GoFundMe

"I donated because she was such a little bundle of joy. I always felt happier whenever I got to see her. I will forever cherish her in my heart," one person wrote.

"I am so sorry for your loss. You remain in my thoughts and prayers. May you find the strength to get through this," another said.

It comes just a week after newborn twins were mauled to death after the family dog turned violent in Brazil.

Anne and Analú, died on June 23, the day they were scheduled to be born by caesarean, having arrived a month early.

Shocked relatives said the dog, a labrador and American foxhound cross, had been the family's pet for five years and was usually docile.

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The dog is believed to have become jealous after losing affection from his owners.