TORONTO -- A six-year-old girl is dead after she drowned in a backyard pool at a home in Oshawa during a party on Saturday night.

Durham Regional Police say that they were called to a home in the Birchview and Ormond drives area at 7 p.m. for reports of a large gathering taking place.

“After police arrived, they were advised that a six-year-old female was missing. Police started to search the property and located the female victim in the pool,” police said on Sunday.

An officer dove into the pool and brought the girl to the surface, where officers performed CPR until paramedics arrived.

She was then rushed to a local hospital where she was later pronounced dead.

An investigation into the circumstances surrounding her death is underway.

A man who lives nearby told CP24 that a woman was going door to door prior to emergency crews’ arrival, telling them that a small child was missing and asking them to check around their properties for any sign of her.

Police arrived a short time later, along with their helicopter.

The owner of the home where the drowning occurred told CTV News Toronto she was holding a fifth birthday party for her daughter.

“It's horrifying,” she said. “A good thing turned horribly wrong and it's something we have to live with.”

When attendees realized the six-year-old girl was missing, they could not see her in the pool and instead thought she was missing somewhere in the neighbourhood.

“The first thing I said was, did you guys check the pool? They said, Yeah, for sure [she’s] not in the pool," the owner said.

“Everyone in this area was looking for her, not knowing this whole time the little girl was in the pool.”

Police did not locate the girl in the pool until more than one hour after she was first thought to be missing.

“(Durham Regional Police Service) continues to support the family during this horrible tragedy and encourage all families to exercise extreme care when dealing with water safety during the summer months,” police said Sunday.

Anyone with information is asked to call Det. Const. Kollaard at 1-888-579-1520. ext 1614.