Click to see more PAT chief Tahirul Qadri leads funeral prayers for murder victim in Kasur.
Rights activist Farzana Bari observed that people "feel unsafe" and "have lost all trust in state institutions".
"These people that are protesting do not have a leader, they are not being led," she pointed out. "They are all protesting because they feel unsafe."
Pakistan Tehreek-i-Insaf (PTI) leader Mian Mehmoodur Rasheed while speaking to DawnNews said the culprits in such cases should be handed capital punishments so that such incidents don't occur again.
PTI's chief whip Shireen Mazari at a press conference in Islamabad raised questions over the conduct of police in the city.
"Where was the police when the girl went missing?" she asked.
Pakistan Awami Tehreek leader Tahirul Qadri led the funeral prayers for the victim, with thousands of residents of the city gathered to lay the child to rest.
'Unforgivable' incident Lahore High Court (LHC) Chief Justice Mansoor Ali Shah, Punjab CM Shahbaz Sharif and the Senate Standing Committee on Interior, taking notice of the incident earlier in the day, ordered the Punjab police to take swift action.
Sharif directed the inspector general of Punjab to bring the culprits to task as soon as possible and to submit an investigation report on the matter.
The Punjab chief minister later in the day made district police officer Kasur an officer on special duty (OSD), a Punjab government spokesman said. Sharif also constituted a joint investigation team (JIT) headed by Additional IG (Investigation) Abu Bakar Khuda Bux to investigate the incident and submit a report within 24 hours.
"I will not rest until justice has been provided to the affected family," Sharif was quoted as saying.
Senate Committee Chairman Rehman Malik called the incident unforgivable and ordered that the Punjab police submit a report on the matter within the next five days.
Malik also said that the Inspector General of Punjab should personally investigate the matter and treat it as a challenge.
Chief of Army Staff Gen Qamar Bajwa condemned the "cold-blooded murder" and directed immediate support to the civil administration to arrest the criminals and bring them to justice, the army's media wing tweeted .
The Jamiat Ulema-i-Islam-Fazl on Wednesday presented adjournment motions in the Senate and the National Assembly to discuss the failure of the government and local law enforcers to recover Zainab.
"The tragedy happened because the girl was not recovered in time," the adjournment motion claimed. "This is not the first time such an incident has taken place in Kasur."
By Wednesday evening, the Chief Justice of Pakistan, Mian Saqib Nisar, had taken notice of the incident and sought a report from the Inspector General of Police, Punjab, within 24 hours.
'Must strengthen system to avoid such crimes' Senate Chairman Raza Rabbani suggested introducing appropriate legislation and stricter legal implementation in order to prevent such incidents in the future.
"All institutions must work together, and implementation of laws must be strengthened," he said.
Rabbani said that when the Kasur child abuse scandal surfaced in 2015, he had raised concerns that the outrage would die down within a few days, which is why it is necessary that the government take long-term measures to ensure the safety of children.
"Institutions and the government must work together on operational procedures for such incidents," he said, adding that laws and a permanent institution must be introduced to deal with these crimes.
Laws for the protection of children must be made in line with international laws, he said. Existing laws that deal with crimes against women could possibly be expanded to include crimes against children, he suggested.
Laws tackling crimes against children must tackle brutality, child smuggling and different kinds of abuse, including sexual abuse, he recommended, adding that stronger legal implementation and punishment of criminals is necessary to avoid such incidents from occurring.
Kasur had last attained local and international notoriety in 2015 when a gang of paedophiles running a child sex ring was busted in the city.
The gang had allegedly abducted and sexually assaulted at least 280 children in the area, had blackmailed the families of the victims since 2009, and even sold video clips and images of the assault online.
With additional reporting by Fahad Chaudhry in Islamabad and Saifullah Cheema in Lahore.