The frantic 911 calls of the neighbor who discovered a mother who shot her family in the wreckage of her pickup truck have been released by detectives.

Police believe Suzanna Simpson, from South Carolina, shot and killed her five-year-old son and seven-year-old daughter in their beds and seriously wounded her husband, before crashing her truck into trees outside the family home in Pickens County on Tuesday morning.

The man who found the injured woman, 35, told the operator 'something's not right here', when neither Simpson's husband nor her children answered his urgent knocking at their front door.

In the recordings released by police, Simpson can be heard moaning in the background as her neighbor tells the operator: 'She's responding, but she's been knocked unconscious.

'She's run off the road... she's taken down some trees,' he says.

After trying and failing to get an answer at the family home, the man made a second 911 call and told the operator: 'Something's not right here...this lady in the truck is my neighbor... her husband's truck is still in the yard.

'I can't get her husband or kids to the door,' the man said.

'We need somebody here to check this house.'

Police found Simpson's five-year-old son Sawyer and her seven-year-old daughter Carly lying dead in their bedrooms after the woman told stunned paramedics attending the crash scene 'OK, OK, I shot my whole family'.

Her husband Michael, 34, was shot in the head while in bed. He is in hospital suffering life-threatening injuries.

After leaving the house, Simpson's truck crashed into a tree with such force its roots were lifted from the ground, according to a Fox News report.

Pickens Country Sheriff's Office has revealed that Simpson told a nurse at the hospital she wanted to kill herself, but just couldn't do it.

'I shot my kids, then my husband and tried to shoot myself several times but couldn't do it,' said Simpson at Greenville Memorial Hospital according to the arrest warrant.

Deputies are still trying to figure out what happened and why Simpson decided to shoot her family, Pickens County Sheriff Rick Clark said at a news conference.

'I can tell you honestly that we have no idea at this time,' said Clark.

Suzanna Simpson has been charged with two counts of murder and attempted murder. She is also at the hospital, but Clark would not talk about what injuries the 35-year-old mother might have suffered or how seriously she was hurt.

Clark said it is likely many details in the shooting won't be released until Simpson appears in court.

Walt Wilkins, 13th Judicial Circuit solicitor, said the shootings could lead to seeking the death penalty because the case involves children and multiple deaths.

It isn't known if Simpson has an attorney.

In a statement Tuesday, school Principal Michael Fleming said: 'Dacusville Elementary is deeply saddened by the loss of two of our children, Carly and Sawyer Simpson.

'Both students were very special to the faculty, staff, and children of our school. Carly had a beautiful smile that brightened everyone's day. Sawyer's excitement for learning was contagious. Our heartfelt condolences go to the family.'

Carly's first-grade teacher, Nancy Zeigler, described Carly as 'sweetness defined,' to The Independent Mail

'She was a very smart little girl who loved to help her fellow classmates,' said Zeigler.

'She was a leader in the classroom and loved by all.'

Sawyer's kindergarten teacher, Jama Freeman, told the Independent Mail he was 'enthusiastic, adventurous and creative.'

The family's home is in the Dacusville community, about 15 miles northwest of Greenville.

The killings came less than two years after a 49-year-old woman killed her two adult sons, her ex-husband and her stepmother in their Pickens County home.

Susan Hendricks pleaded guilty but mentally ill to the murders last month and was sentenced to life in prison. The sheriff said another slaying involving a mother killing her children weighed heavy on his officers and the county of 120,000 people.

'No matter how tough a cop you are, no matter how many people you have prosecuted — doesn't matter who you are,' Clark said.

'When kids are involved it's a whole different situation. It has gotten to us today.'