Security forces cordoned off the area on Bedian Road in the bustling capital of Punjab province after the blast.
Security forces cordoned off the area on Bedian Road in the bustling capital of Punjab province after the blast, which rescuers said occurred just before 8:00 am local time. A forensics team could also be seen at the site.
The Tehreek-e-Taliban Pakistan (TTP, or Pakistani Taliban) claimed responsibility for the attack in a message sent to AFP.
"It appears to have been an act of terrorism," Punjab provincial law minister Rana Sanaullah said in televised comments, though other officials cautioned they were still investigating the nature of the blast.
Punjab health minister Khawaja Imran Nazir said five people had been killed, with the toll confirmed by a security source and a Lahore administration official.
A police official said the census team had been the target, though the Pakistan Board of Statistics declined to comment. The TTP in its statement said it had carried out the attack in revenge on security forces.
Teams of enumerators backed by the military and security forces are carrying out Pakistan's first census in almost two decades, an enormous and highly charged task that could redraw the country's political map one year before national parliamentary elections.
The police official said at least 10 people had been wounded, though rescuers gave a higher figure of 18.
Some officials initially described the incident as a gas cylinder explosion, but said an investigation was ongoing. There was no immediate comment from the military.
"There is a possibility that it was a suicide attack," Lahore official Abdullah Sumbal said.
"The census is a national duty, and we will complete this task," he added. "There was no lack of security, but you know how difficult it is to deal with suicide attacks."
Lahore has been on edge since a wave of violent attacks across Pakistan in February killed 130 people and shook citizens emboldened by growing security.
The attacks included a bomb blast in the eastern city on February 13 which killed 14 people in an assault claimed by Jamaat-ul-Ahrar (JuA), a faction of the Pakistani Taliban.
Ten days later a fresh blast sent panic through the city when it killed eight people, though officials later said it was a gas leak, not an attack as initially feared.
Wednesday's explosion came days after at least 22 people were killed and 57 wounded on March 31, when a car bomb tore through a market in a mainly Shiite area of Pakistan's tribal belt in an attack that was also claimed by JuA.
February's assaults also included a suicide blast at a Sufi shrine in Sindh province which killed 90 people and was claimed by Islamic State.
The wave of violence has dented optimism after the country appeared to be making strong gains in its decade-and-a-half long war on militancy, with analysts speaking of a militant resurgence.
The powerful military launched a nationwide crackdown, killing dozens of alleged militants across the country.
Islamabad also swiftly accused neighbour Afghanistan of harbouring militants responsible for the attacks, and temporarily closed the border between the two countries.
Kabul has long accused Pakistan of harbouring the Afghan Taliban, a charge which Islamabad has at times admitted to.