A four-year-old boy has died days after being accidentally shot in the head by a handgun tucked into his father's pants, police said.

Tripp Shaw, of Indiana, was injured on Sunday night last week when a Glock semi-automatic handgun that his dad Tyler had tucked in the small of his back discharged while they play-wrestled on a bed in their Bloomington home, the New York Post reported.

The Monroe County Sheriff's Office reported the young boy died on Thursday, according to indystar.com.

Tripp's dad, Tyler Shaw, 36, was struck in the head with the same bullet that killed his son. His injuries were not life-threatening.

Sheriff Brad Swain said the boy's mother and two-year-old sister were also in the house when the gun discharged, indystar reported. Authorities sent the Glock off to be tested for any defects that may have caused it to fire unexpectedly.

One of the family's next-door neighbours, Kaili Frye, told CNN affiliate WXIN, "It's horrifying. It's heart-wrenching. I can't even imagine what they are going through."

Friends of the Shaws have launched a crowd-funding drive to "help with the financial stress."

The GoFundMe campaign - called #ShawStrong - notes "It takes a village to help through an accidental tragedy. The Shaw family has been through so much in this situation."

Since being started four days ago, the campaign has raised $US20,986 ($A30,700).

Over the weekend, fundraiser organiser Brandi Conder wrote, "It is with great sadness that I update the Tripp passed away yesterday morning. Little Tripp passed away peacefully, surround by those who loved him the most.

"Please give the family time to process this & grieve. Continue to pray for Tyler, Natalie, the girls and the extended family."

Indiana is an open carry state, with a permit. It's not known if any criminal charges will be filed in connection with the shooting, indystar reported.

- with staff writers

This article originally appeared on the NY Post and was reproduced with permission