A woman was severely burned after being covered in gasoline and set on fire by her knife-wielding ex-boyfriend and father of her child, police said.

The 34-year-old, who has not been named, suffered the horrific attack outside a 7-Eleven store in South Florida following a row with Roosevely Mondesir, when they met so that she could pick up her son.

She was waiting outside the store in her silver Mercedes at around 3am on Monday when Mondesir showed up in his white Jaguar without the boy and began hurling the fuel over her, Boynton Beach Police spokeswoman Stephanie Slater said.

She tried to run away, but the 52-year-old man chased her with a knife and then ignited her.

In graphic surveillance video, a man can be seen threatening a woman with a large knife, struggling in the doorway of the store.

'Get away from me!' she can be heard shouting.

They disappear from view until she returns in a massive fireball, screaming and running around the parking lot.

Officers searched by foot, with a police dog, and by helicopter before finding Mondesir several hours later in bushes near the 7-Eleven.

He was charged with attempted first-degree murder and was being treated for burns at Bethesda Memorial Hospital in Boynton Beach before being transferred to jail.

It was not known if he had yet obtained an attorney.

The victim was not identified, but she is expected to survive. She was being treated at Delray Medical Center.

Police haven't said what led to the attack.