A large number of people including Christians were present in the Gulshan-e-Iqbal Park in Iqbal Town area of the city when the blast occurred, leaving many in a pool of blood.
"It was a powerful blast. It is suspected that a suicide bomber blew himself up at the gate of the main gate of the park," Deputy Inspector General Lahore Police Haider Asharaf said.
The park is located in a posh-locality in Lahore, the hometown of Prime Minister Nawaz Sharif. The city is comparatively peaceful in an otherwise violence-wracked Pakistan.
Eyewitnesses said there were scattered body parts in the park, where a large number of families, especially women and children, were present on a Sunday evening. The crowd was "unusually large" because of Easter.
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"Still a good number of people are in critical condition," Punjab Emergency Services Rescue 1122 spokesperson Deeba Shahnaz said.
Over 100 injured have been shifted to different hospitals of Lahore, she said. Doctors said the death toll may rise.
Children and women were among the dead.
"My two children were on the swing when a powerful blast occurred. The children and I fell on the ground. I was semi-unconscious. When I fully regained consciousness, I ran to find my children. Thank God, they were alive and have injuries on their head," one of the victims, Saleem Shahid, said at Mayo Hospital.
A heavy contingent of police has cordoned off the area.