A woman was burned alive by her ex-boyfriend after she left him.

A young woman has died after her ex-boyfriend allegedly doused her in alcohol before setting her alight.

Student Sara Di Pietrantonio, 22, died on Sunday after she was burned alive in a side street in Rome, Italy.

The Sydney Morning Herald reported Prosecutor Maria Monteleone told reporters that Vincenzo Paduano, 27, first set her car alight before he set her ablaze too.

Investigators said a cigarette lighter had been used to start the blaze on the 22-year-old’s face after it had been doused in alcohol.

Lead police official in the investigation, Luigi Silipo, said the crime was stand out in its gruesome details.

"I can say that in 25 years in this work I have never seen something so atrocious," he said.

Silipo said the accused walked off his job as a security guard to wait outside the house of Di Pietrantonio's new boyfriend.

The police official said that Paduano followed the 22-year-old when she left her new boyfriend's house before forcing her to pull over into a side street.

"He got into her car, and after an argument, doused the car (interior) with a small bottle of alcohol, and doused Sara, too," Silipo said.

"She ran out, he torched the car, caught up with her."

The police official said the young woman was left to die "in an atrocious manner".

Italian authorities said a nearby surveillance camera captured at least two cars had driven past while the woman screamed for help.

Prosecutor Monteleone said the woman's life may have been saved if passersby had have stepped in.

Monteleone used the case as a springboard to raise awareness around domestic violence in the Italian community.

The prosecutor urged women "not to keep hidden any threatening behaviour by those who insist they love you, but it's not that way."

Monteleone said Paduano is currently being held for investigation of premeditated murder.