The blast took place on a street parallel to where participants dressed in colorful folkloric costumes were making their entrance to the Carnival in the city of Oruro, said police deputy commander Freddy Betancurt. Among the dead were two children.
Betancurt said police believe the explosion was caused by hot oil weakening the hose to the vendor's gas canister. The expansive wave from the blast carried out at least 50 yards (meters).
He initially reported six people dead and 13 injured, but regional police Commander Romel Rana later raised the number of injured to at least 28.
President Evo Morales lamented the accident on his Twitter account and said his government would help the injured.
"I'm very dismayed by news of the deaths from the explosion of the gas tank near the Folkloric Entrance to the Oruro Carnival," he tweeted.
Oruro's Carnival draws tourists from Bolivia and around the world, and was declared a world heritage site by UNESCO.
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