The explosion took place near the children's rides in Gulshan-e-Iqbal park - which was crowded with Christians celebrating Easter -local police chief Haider Ashraf said. He said the explosion appeared to have been a suicide bombing, but investigations were ongoing.
Lahore district government official Mohammad Usman said he believed the park was struck because it is a "soft target," and not because of the Christian celebrations. He did not elaborate.
Zaeem Qadri, a spokesman for the Punjab provincial government, said the wounded had been taken to six hospitals in Lahore. Punjab's chief minister Shahbaz Sharif announced three days of mourning and pledged to bring the perpetrators to justice, Qadri said.
The park was manned by police and private security guards, police chief Ashraf said. "We are in a warlike situation and there is always a general threat but no specific threat alert was received for this place," he added.
Salman Rafiq, a health adviser to the Punjab government, called on people to donate blood, saying many of those wounded were in a critical condition.
Footage broadcast on local television stations showed chaotic scenes in the park, with people running while carrying children and cradling the wounded in their laps.
A witness, not identified by name on Pakistan's Geo TV station, said he was heading toward a fairground ride with his wife and two children when he heard a huge bang and all four of them were thrown to the floor. A woman was shown crying while looking desperately for her missing five-year-old son.
A spokesman for the U.S. National Security Council said that the United States "condemns the attack in the strongest terms," describing it as a "cowardly act in what has long been a scenic and placid park." Ned Price said the U.S. would continue to work with Pakistan and its partners to "root out the scourge of terrorism."