CHICAGO (AP) — A fire at a Chicago apartment building that appears to have been deliberately set killed four people Tuesday, including three children, police said.

Chicago firefighters battle an apartment fire in the 8100 block of South Essex Avenue in the South Chicago neighborhood early on Tuesday, Aug. 23, 2016. The fire at a Chicago apartment building that appears to have been deliberately set killed multiple people Tuesday, police said. (Alexandra Chachkevitch/Chicago Tribune via AP)

Chicago firefighters battle an apartment fire in the 8100 block of South Essex Avenue in the South Chicago neighborhood early on Tuesday, Aug. 23, 2016. The fire at a Chicago apartment building that appears to have been deliberately set killed multiple people Tuesday, police said. (Alexandra Chachkevitch/Chicago Tribune via AP)

The fire began around 1:30 a.m. in a three-story building in the South Chicago neighborhood.

A preliminary investigation indicates a person returned to the building after a domestic dispute and set fire to the rear porch, police spokesman Anthony Guglielmi said.

Officers are searching for a “person of interest wanted for questioning,” he said.

Charred and broken widows can be seen on the third floor of an apartment building where a fire that appears to have been deliberately set, killed multiple people, Tuesday, Aug. 23, 2016, in Chicago. (AP Photo/M. Spencer Green)

Charred and broken widows can be seen on the third floor of an apartment building where a fire that appears to have been deliberately set, killed multiple people, Tuesday, Aug. 23, 2016, in Chicago. (AP Photo/M. Spencer Green)

An emailed police statement said a 3-month-old was pronounced dead at a hospital and two other children and a man were found dead later at the scene.

Three other people have been hospitalized, according to the Chicago Fire Department’s media office.

Witnesses told reporters they saw several people jumping from windows to escape.

Chicago firefighters battle an apartment fire in the 8100 block of South Essex Avenue in the South Chicago neighborhood early on Tuesday, Aug. 23, 2016. The fire at a Chicago apartment building that appears to have been deliberately set killed multiple people Tuesday, police said. (Alexandra Chachkevitch/Chicago Tribune via AP)

Chicago firefighters battle an apartment fire in the 8100 block of South Essex Avenue in the South Chicago neighborhood early on Tuesday, Aug. 23, 2016. The fire at a Chicago apartment building that appears to have been deliberately set killed multiple people Tuesday, police said. (Alexandra Chachkevitch/Chicago Tribune via AP)

Clay Turner said he saw a man screaming for help on the ground with the 3-month-old next to him. He told the Chicago Tribune he ran to them and tried to help.

“I’m just speechless,” Turner said.

Bystanders look at the scene of a fatal fire early on Tuesday, Aug. 23, 2016, in the 8100 block of South Essex Avenue in Chicago.The fire at a Chicago apartment building that appears to have been deliberately set killed multiple people Tuesday, police said. (Nancy Stone/Chicago Tribune via AP)

Bystanders look at the scene of a fatal fire early on Tuesday, Aug. 23, 2016, in the 8100 block of South Essex Avenue in Chicago.The fire at a Chicago apartment building that appears to have been deliberately set killed multiple people Tuesday, police said. (Nancy Stone/Chicago Tribune via AP)

A resident, 25-year-old Lanita Smith, told the newspaper that she woke up to loud noises and thought someone was breaking in to her apartment. But then she saw her kitchen door was on fire.

“The fire was upstairs and downstairs,” she said. “My whole porch was on fire.”