A 3-year-old girl here in the US state of Texas has shot and killed her 4-year-old sister after she gained access to a loaded semi-automatic gun, in the latest instance of a child using an unsecured firearm and causing a tragedy.

The incident took place on Sunday when the two children were in their apartment in North Houston with five adults, the Houston Chronicle newspaper reported.

The three-year-old gained access to a firearm and "unintentionally" shot and killed her 4-year-old sister late Sunday, Harris County Sheriff Ed Gonzalez said.

Gonzalez said the preliminary investigation showed that the two children were inside an apartment with five family members and friends and each of the two children's parents believed the other was watching the kids.

Instead, they were left unsupervised and picked up an "unsecured" and loaded semi-automatic pistol, the report said.

The family members heard one gunshot and ran into the room to find one child had apparently accidentally shot the other toddler, Gonzalez said at a press conference.

The injured child was unresponsive, he said, and the parents immediately called 911.

Gonzalez urged people to ensure their guns are stored where kids cannot reach them, especially entering spring break week, when more kids will be at home.

'You've got to make sure you're a responsible gun owner. Secure your weapons in a safe place. It's got to be more than just to tell the kids not to touch the weapons," Gonzalez was quoted as saying by the 6abc.com portal.

Officials said it is not clear at this point if anyone will face charges.

The shooting is just the latest instance of a child using an unsecured firearm and causing a tragedy. The most prominent such shooting recently involved a 6-year-old boy who shot his elementary school teacher earlier this year in Newport News, Virginia; the teacher is recovering, CNN reported.

There were at least 2,070 unintentional shootings by children under 18 years old between 2015 and 2020, resulting in 765 deaths and 1,366 injuries, according to data compiled by Everytown Research & Policy, the research arm of the group that advocates for gun control and against gun violence. About 39 per cent involved a shooter 9 years old or younger, the non-profit said.

Firearm-related injury recently surpassed motor vehicle crashes to become the leading cause of death among people 1 to 19 years old in the US, according to a 2022 paper published in The New England Journal of Medicine. In that, the US stands alone among world powers.

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