Police have confirmed the blast occurred the tanker crashed in the Morogoro region, 124 miles west of port city of Dar es Salaam.
Morogoro is on a major route for transporting cargo and fuel from the very busy port.
Reportedly a crowd was gathered around the crash as people siphoned fuel from the tanker.
Pictures on social media show dozens of charred bodies amongst the wreckage.
Video also appears to show a large crowd gathered around the tanker moments before the explosion.
It is believed another 65 are injured after the vehicle blew up
Regional police commissioner Steven Kabwe told local Azam TV that 57 bodies had so far been recovered.
There are fears the death toll could rise after the violent explosion.
State broadcaster TBC Taifa reports some victims were siphoning petrol from the vehicle.
Government spokesman Hassan Abbasi said: “We have been saddened by reports of an accident involving a fuel truck in Morogoro, which caught fire and burned several people.”
Footage from before the explosion showed a large crowd collecting liquid from puddles in yellow jerry cans after the vehicle crashed.
Video clips from the accident scene circulating on social media show the charred remains of dozens of young men and motorbikes.
The situation is really bad. Many people died, here even those who were not stealing fuel because this is a busy place,” Daniel Ngogo, an eye witness said.
“The fire was huge and it was challenging to rescue victims.
“I have seen about 65 to 70 people being rescued because the fire was fast spreading across the accident area.”