- The Pakistan Taliban has claimed responsibility for the incident
The assailants targeted members of the security services who were carrying out the national census -- Pakistan's first in 20 years -- said Malik Muhammad Ahmed Khan, a spokesman for the state government of Punjab.
Another two people are in critical condition, he said.
Prime Minister Nawaz Sharif issued a statement expressing his condolences to the victims.
The Pakistan Taliban, whose objective is to establish Sharia law in Pakistan, claimed responsibility for the bombing, spokesman Mohammed Khurrassani said in a phone call with CNN.
The group is responsible for the deaths of scores of people in a series of attacks across Pakistan's remote border with Afghanistan, including the 2012 attack on Nobel laureate Malala Yousafzai and the 2014 Peshawar school massacre in which 145 people were killed, including 132 children.
CORRECTION: A previous version of this story incorrectly described a statement by the Islamic State Khorashan. That group, an ISIS affiliate, claimed credit for a separate attack in Sehwan in February.