A video posted on social media showed dozens of people carrying yellow jerricans around the truck.
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".
At least 57 people are killed in a fuel tanker explosion in eastern Tanzania, authorities have confirmed.
"There are vehicles that carry unsafe fuel oil, as in this case in Morogoro, there are others that carry toxic chemicals or explosives, let's stop this practice, please", he said.
Reportedly a crowd was gathered around the crash as people siphoned fuel from the tanker.
Morogoro is located approximately 120 miles from Tanzania's economic hub of Dar es Salaam. They said people were trying to siphon away fuel when the tanker burst into flames.
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"The situation is really bad", Daniel Ngogo, an eye witness, told Reuters.
'The fire was huge and it was challenging to rescue victims.
The road connecting Morogoro with Dar es Salaam is on a major route for transporting cargo and fuel from the port, which is the country's commercial capital.
People getting killed in explosions while stealing fuel from incapacitated tankers are fairly frequent in East Africa, though the Saturday explosion is among the deadliest in Tanzania.
Almost 80 people died in May in a similar incident near the airport of Niger's capital Niamey.