Police said the explosion occurred in the main market area just before a meet-and-greet event of candidate Mufti Syed Janan, who reportedly was the target, Geo News reported.
Janan was uninjured, officials said. The explosion occurred near his vehicle.
Geo News said an unknown number of people were injured.
Political parties and candidates have been targeted since campaigning began last month in advance of the general election Saturday.
Imran Khan, a former cricket star running as a member of the Pakistan Tehrik e Insaf party, was slightly injured Tuesday when he fell off an elevator taking him to a stage at a campaign event in Lahore.
Officials said Kahn and two guards were on the elevator when the guards lost their balance and all three men fell. Khan had a slight head injury that required stitches and was taken to a hospital. The extent of the injuries to the guards wasn't known.
A PTI spokesman said Khan would resume campaigning in a few days.
Hundreds of supporters gathered at the hospital after it became known Khan was was being treated there.