Haiti Prime Minister Garry Conille visited the site, near the coastal city of Miragoane in the department of Nippes, and said some of the most seriously injured victims were evacuated by helicopter to receive medical care.
"This is a horrible scene, what I have just witnessed," he said in a statement.
Earlier, Conille said emergency teams were working to "save the lives of the seriously injured," and pledged government support for the victims and their families.
Media outlet Radio RFM said 25 people died in the incident that took place early Sunday AEST. Earlier, authorities in Nippes said 16 bodies were completely charred and unrecognisable, and 40 people had been taken to the local hospital with burns.
Haiti Prime Minister Garry Conille visited the site of the explosion. (AP PHOTO)
Images released by the government show medical staff helping a man whose legs and head were swathed in white bandages, as he entered a humanitarian air service helicopter.
A witness to the incident said the truck's fuel tank had been punctured by another vehicle, and people rushed to the site to collect fuel.
"There were a lot of people. Those who were close to the truck got pulverised," said the man, who did not give his name, in a video interview with local outlet Echo Haiti Media.
When asked how many people might have been killed in the blast, he said it was difficult to say.
"You can't know, because there were a lot of people, bystanders and those collecting oil. There were a lot of people," he said.
Fuel deliveries to the Miragoane area have slowed in recent weeks as trucks were transported via ferry to avoid gang-controlled highways surrounding the capital of Port-au-Prince.
The spread of gangs in the capital and surrounding areas has fuelled a humanitarian crisis with mass displacements, sexual violence, child recruitment and widespread hunger. A state of emergency is now in place nationwide.
Haiti's civil protection agency reported the identities of a 31-year-old man and two 23-year-old men who suffered burns over 89 per cent of their bodies, and were being treated in a hospital in Les Cayes, in southern Haiti.
Two of them sustained second-degree burns, the agency said.
A similar incident in 2021 in the city of Cap-Haitien killed at least 60 people, after people were also thought to have been attempting to take fuel from a tanker truck.
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