Detectives are investigating after a 5-year-old boy fell ill and died Sunday at a Pilsen migrant shelter where he was living.

A Chicago police spokesperson said an investigation is underway, but it does not appear as though the boy’s death was criminal in nature.

The boy — whom the Cook County Medical Examiner’s Office identified as Jean Carlos   Martinez Rivero — was not feeling well when he was rushed to Comer Children's Hospital at around 2:45 p.m. Sunday.

Police said he later died at the hospital. No one has been taken into custody.

Mayor Brandon Johnson said in a statement Monday that, according to initial reports, it appeared the boy was suffering from a medical emergency. According to Johnson, officials are providing support to the family and are still gathering information on this tragedy.

“My heart and my prayers go out to the Martinez family,” Johnson said. “The City will continue to provide resources and support to them during this difficult time.”

The Chicago Sun-Times reported that migrants at that shelter have complained of overcrowding with many sick people living there.

Since August 2022, 600 buses have arrived in Chicago, carrying nearly 26,000 people, nearly all of them who fled economic collapse and political turmoil in Central and South America. More than 80% have arrived after Johnson was inaugurated, according to city data.

At least four other children and teens became ill at the migrant center, according to the Chicago Fire Department, including a 1-year-old girl who was hospitalized with a fever.

An 18-year-old woman, 8-year-old girl and 4-year-old girl also all reported fevers.

Although the city reports that police stations have been mostly cleared, massive shelters are not necessarily a safe alternative, said Annie Gomberg, a volunteer with the city's Police Station Response Team who has been working with Chicago's new arrivals since April. Gomberg said about 2,300 people have been staying at the shelter where the boy was living.

“The shelters are completely locked down to outside access. They’re doing this allegedly in order to protect the residents inside,” Gomberg said. But she said she suspects part of the reason for tight security is so the public cannot see how the shelters are being run.

“The people who live inside are coming to us and saying, ‘please give us blankets, give us clothing for our children, we need bottles, we need diapers,’” she said.

Gomberg sent The Associated Press videos taken by shelter residents showing coughing and crying children in the crowded Pilsen shelter where Martinez was staying. One video showed water leaking from the ceiling onto the cots below.

Gomberg said people staying there told her mold is visible in the shelter, and lack of insulation makes the repurposed warehouse very cold. One of the photos shows a toddler wearing a snow suit and winter hat indoors.

“If you know Chicago at all, this is really when the rubber meets the road," she said. “We could very easily have paralyzing snowstorms. We could very easily have below zero temperatures.”

Illinois State Rep. Delia Ramirez called the boy’s death “unacceptable and devastating.”

“My heart and prayers are with his family,” she said in a statement. “It is heartbreaking that substandard care, under-resourcing, and years of political inaction continue to steal bright futures and rob families and our communities of possibilities.”

Ramirez said she’s spoken with city officials, who believe there must be a full investigation into Favorite Staffing — the Kansas-based company that’s contracted to run Chicago shelters — can “fulfill the important responsibility of providing safe and adequate temporary shelter for migrants and asylum seekers.”

The Associated Press contributed to this report.