Police in Pakistan said on Tuesday they had arrested a man suspected to be a serial killer responsible for the rape and murder of a seven-year-old girl, a case that ignited nationwide protests over allegations of government inaction.

Police found Zainab Ansari's body in a garbage dumpster in Kasur district near the eastern city of Lahore last week, four days after she was reported missing. Residents of the area have said the murder was the 12th such incident in a year, setting off fears of a serial rapist killer on the loose.

Shahbaz Sharif, chief minister of Punjab province, where Kasur is located, said the arrested man had confessed to Zainab's murder and his DNA matched samples found on her body.

Sharif, addressing the media, identified Imran Ali, 24, of Kasur, as the killer of Zainab.

Regional police officer Zulfiqar Hameed told Reuters the suspect was one of Zainab's neighbours. CCTV footage of the day she was abducted showed her walking off calmly with a man identified as her kidnapper.

A police official who asked not to be named said the accused had confessed to multiple murders and that he was suspected of raping and killing at least seven girls.

He added that Ali was arrested on Wednesday but police waited to match DNA evidence before making an announcement.

Sharif said in his statement that 1,150 DNA samples were collected and matched with samples taken from Zainab's body. Two people were killed in Kasur the day after Zainab's body was recovered when police fired at hundreds of angry protesters, who said negligence on the part of the authorities was behind the repeated killings.

A number of police officials have been transferred out of Punjab for failing to investigate complaints of missing children since 2015, when authorities uncovered what they said was a paedophile ring linked to a prominent local family.

At least two people have been convicted in connection with that case, in which authorities say hundreds of children in the district were abused.

A total of 1,764 cases of child abuse were reported across Pakistan in the first six months of 2017, according to Sahil, an organisation that works on child protection. In 2016, the total number of reported child abuse cases was 4,139, or around 11 new cases reported per day.

Zainab's case has emotions running high in Pakistan and the normally taboo subject of child abuse being discussed widely on local television.

"I want Imran Ali to be hanged publicly ... I will request the political parties to support my wish," Sharif said.