Two young children have been shot by their siblings in the space of 24 hours in the United States.

In Las Vegas, a two-year-old girl was in a critical condition after being shot by her four-year-old brother at their home, police said.

In South Carolina, a four-year-old boy was shot in the stomach by his three-year-old brother after the little boy found a gun. The injured boy was expected to make a full recovery.

The incident in Las Vegas happened on Thursday night when the girl's brother found a loaded 9mm handgun in their home. It went off while he was holding it, hitting his sister in her torso. According to police, the father was at home at the time and the gun appears to have been improperly secured.

The shooting involving the two brothers happened in Gray Court, South Carolina, also on Thursday night. They and their father were staying at the home of a family friend.

Laurens county sheriff Ricky Chastain said it appeared the younger boy found the gun under a bed and accidentally shot his brother. The injured boy was flown to hospital, where he underwent surgery, he said.

No charges have been filed in either case.

The two incidents come less than a week after a five-year-old boy died after shooting himself in the head. He had found a handgun inside his father's vehicle outside a Las Vegas pharmacy.

The father in that case has been charged with child endangerment.

The right to bear arms is enshrined in the second amendment of the US constitution. There are thought to be more than 200 million firearms in private hands.

Advocates of gun control face tough opposition from gun owners. Critics of the current gun laws link high levels of gun crime and gun-related injury with high levels of gun ownership.