Khan, chairman of Pakistan Tehrik-e-Insaf (PTI), fell off a lifter while he was being raised to a stage to address an election rally, his spokesman Ejaz Chaudhry said.
Chaudhry said that the PTI chief received injuries at the forehead but said he is out of danger, reported Xinhua.
TV footage showed Khan was taken to hospital while bleeding continued from his forehead.
He was first taken to a local hospital for stitches and later was transferred to his own Shaukat Khanum Hospital for further treatment, PTI leader Asad Umar said.
Witnesses said that Khan came down from nearly a 20-feet lifter
A witness said that Imran Khan hit a rod as he came down and bleeding started from his forehead.
PTI leader Dr Yasmin Rashid also said that Khan is conscious and is talking, which is a good sign in case of head injuries. She said doctors put 16 stitches.
Another party leader Asad Omar said that Imran Khan was talking to the doctors and he was confident.
He said that Khan will not address the public meeting Tuesday night and will take a rest. He appealed to the people to pray for him. He told Khan's supporters that there is no need to panic.
Police held Khan's security guard responsible for the incident in preliminary investigation. Police sources said the third guard tried to climb on the lifter that led to its falling down.
Khan's party cancelled all public meetings in Lahore, the party 's spokesman said.
A large number of PTI supporters arrived at Shaukat Khanum Hospital to visit the party leader.
Punjab's Chief Minister Najam Sethi also visited Khan in hospital and inquired about his health.
In their separate messages, President Asif Ali Zardari, Prime Minister Mir Hazar Khan Khoso, Interior Minister Malik Habib Khan, Chief Election Commissioner Fakhruddin G Ibrahim and Pakistan Muslim League (PML-N) chief Nawaz Sharif and other political leaders wished Khan a speedy recovery.