Tuesday's explosion occurred in the Bida area of Niger State after the truck fell and as local residents rushed to the scene to scoop up spilling fuel, police spokesman Wasiu Abiodun said in a statement.
He said 17 people also were injured in the blast and were taken to nearby hospitals.
In recent months, Niger State has seen a rise in accidents involving heavy-duty trucks, which analysts have blamed on bad roads and the absence of a rail network. The state serves as a major transit hub for commodities moving between northern and southern Nigeria.
An investigation was underway to identify the driver, the owner of the tanker and cause of the accident, Abiodun said.
Niger State Governor Umaru Bago said it was disheartening that people go to collect fuel from overturned tankers despite the danger.
"This is yet another painful, difficult, and tragic one for the people and the state government," Bago said.
In January, at least 98 people were killed in Niger State when people tried to transfer fuel from a crashed oil tanker into another truck using a generator.
Scavenging petrol has become common in Nigeria as fuel prices have soared following the removal of subsidies under President Bola Tinubu.
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