TAMPA (Reuters) - A 51-year-old Florida man shot dead his daughter and six grandchildren in his home before killing himself on Thursday, authorities said.

Don Spirit, identified by authorities as the suspect, called the 911 emergency line and killed himself after a sheriff's deputy arrived at the scene, Gilchrist County Sheriff Robert Schultz said.

Everyone in the house was killed, Schultz said. The youngest child was less than three months old and the oldest was 11 years old, he added.

"We're all family here. What can you say?" Schultz said. "There are certain things in life that you can explain, there are certain things that you can't. This is not one that I can explain."

The incident occurred near Bell, a town of about 500 located roughly 35 miles (56 km) west of Gainesville.

The dead woman was identified as Sarah Spirit, 28, the mother of all six of the children, three boys and three girls.

The crime scene was still being investigated on Thursday night.

"We have no indication what caused this man to do what he did," said Schultz. "We may never know."

Schultz said officers had been called to the house before, but there were "no signs or indications to us previously that anything like this could or was going to happen."

Don Spirit, a New Jersey native, had an extensive criminal history, public records show, including convictions for possession of illegal weapons, drug possession, battery and depriving a child of food and shelter.

In 2001, Spirit shot his 8-year-old son to death in what was determined to be a hunting accident, the Orlando Sentinel newspaper reported.

He pleaded guilty to possessing a firearm as a convicted felon in connection with the case and was sentenced in a plea deal to three years in prison, the paper reported.

(The story corrects eldest child's age in paragraph three to 11 from 10.)

(Reporting by David Adams and Jonathan Kaminsky; Editing by Sandra Maler and Eric Walsh)