A Texas judge has granted a mother's request to have sperm harvested from her dead son's body, so she can fulfill his wish of having children.

"I want him to live on. I want to keep a piece of him," Marissa Evans told the Austin American-Statesman newspaper.

Her son Nikolas Colton Evans, 21, died Sunday in hospital after being punched and falling outside an Austin bar on March 27. No arrests have been made in his death.

He had already picked out the names of the three sons he wanted to have some day: Hunter, Tod and Van, said his mother, who had given permission for organs and other tissues to be harvested from his body.

In an emergency hearing Monday, Probate Judge Guy Herman in Austin ordered the county medical examiner's office to continue storing the body at the proper temperature until the sperm could be collected.

Sperm had to be collected within 24 hours of the man being removed from life support unless the body was cooled to no more than 4 C.

While the state gives parents control a child's body for organ and tissue donation, its use for sperm "is very unclear," said University of Texas law professor John Robertson.