Three children died on Sunday morning in Phoenix within the span of one hour after they struggled to breathe, according to police.

A fourth child also died in the nearby suburb of Chandler, Arizona, after experiencing similar symptoms and at around the same time.

Police are still investigating the deaths, which are not believed to be related in any way.

According to The Arizona Republic, police and emergency services were called to a home near Thomas Road and North 32nd Street just before 5:30 a.m. on Sunday.

In that case, a child of an unknown age died at the scene after efforts to revive them were not successful.

At around the same time, a similar call was made and emergency services were dispatched to a home near McDowell Road and North 51st Avenue.

First responders described finding a "very young" child who had stopped breathing.

The child in this case, a toddler, was taken to an area hospital and died there.

One hour later, police received a third call to an apartment complex in the city near the intersection of Broadway Road and Price Road.

As in the other two cases, the child was not breathing, and firefighters attempted life-saving measures that were ultimately unsuccessful.

The child was transported to a hospital and was pronounced dead.

According to KSAZ-TV, a fourth child died in Chandler after emergency services were called to a home in the suburb at 5 a.m. on Sunday.

A five-month-old baby was not breathing and did not survive.

Detective Eva Zermeño with the Chandler Police Department said the infant’s cause of death is being investigated.

"As in any death investigation, we don’t determine the cause of death. Our detectives investigated to see if there was anything criminal that we don’t appear there was at this time. The medical examiner’s office determines the cause of death," Zermeño told KSAZ-TV.

None of the deaths in Phoenix involve "elements that are suspicious in nature, and none include elements of drowning," Phoenix Police Department spokeswoman Melissa Soliz told The Arizona Republic.

There are no additional details available at this time regarding the three deaths in Phoenix and the death in nearby Chandler.

Investigations into each death are ongoing.

This article appeared originally on The Western Journal.