A young mother and her two young children were murdered by her ex-partner while she was on the phone during a desperate 911 call on New Year's Day.

Marissa Reynoso, 26, was shot dead alongside her one- and three-year-old children after her former boyfriend broke in through the back door of her home in South Carolina.

It was the third time she had called police about Jorge Chavez, 25, since their break-up last October, ABC reported. Chavez later killed himself.

Police said that about 40 seconds into the call, Ms Reynoso screamed "he's got a gun!" and the emergency line operator was unable to get her back on the line.

All three bodies were later found in a bedroom, suggesting Ms Reynoso had had no time to hide or barricade herself away, Lexington County Sheriff's Office Captain Adam Myrick said.

ABC said in her first 911 call on 14 November Ms Reynoso had told police her ex-partner, the father of her children, had threatened to kill himself and said to her: "I can't do this anymore. I'll see you in heaven."