The hospital treating many of the wounded, said in a statement that more than 100 people were injured in the blast.
The tanker veered off the road when the driver lost control in Bahawalpur, eastern Pakistan, police official Mohammad Akhtar told CNN.
As the tanker began leaking out profusely, villagers were said to have rushed to the scene to scoop fuel - it exploded in the process.
About 123 people were initially reported dead.
According to CNN, Nishtar Hospital, which is treating many of the wounded, said in a statement that more than 100 people were injured in the blast.
Bahawalpur's Victoria Hospital said it was treating 40 victims, all of whom had suffered burns on at least 70% of their bodies, the report said.
A state of emergency has been declared in the city, Punjab provincial government spokesman Salman Sufi said.
Hospitals have been placed on high alert.