The victim of a gang-rape in Pakistan has died after setting herself on fire in protest against a police report that led to the release of a key suspect, a doctor and her brother said.

College student Amina Bibi died on Friday after dousing herself with petrol and setting it alight on Thursday outside a police station near Muzaffargarh, in Punjab.

"She was under our treatment but she succumbed to her wounds on Friday morning," Muhammad Usman, a local doctor, said, according to Reuters news agency.

The police decision to release the main suspect had been too much for Bibi to handle, her brother said.

"She was already depressed after going through the trauma, but after the release of the accused, she lost all hope of getting justice and set herself on fire," Ghulam Shabir said.

Bibi was raped by five men as she walked home from her college on January 5, he added.

"I was with her when five men kidnapped her at gunpoint and took her away," he said. "I couldn't do anything because they were armed."

Police said they would revisit the case following the death.

"It seems the case had not been properly investigated," said senior police office Chaudhry Asghar. "We have suspended the investigation officer, Rana Zulfiqar, and placed him in detention."

Rape and other forms of sexual assault and domestic violence are widespread in Pakistan, but such public acts of desperation by abused women are rare.