"We have recorded 59 deaths and the searches are still going on," court prosecutor Maiza Compaore told AFP by telephone from the site of the accident near Boromo, 167 kilometres (105 miles) west of the capital Ouagadougou.
"The two vehicles caught fire in the collision," Compaore said earlier. "The scene is gruesome ... there are bodies on the road, some are in the wreckage, there are charred bodies which are still being removed. It's really horrible."
"Only 10 bodies are identifiable, all the rest are badly charred," she said, adding that the bus driver, who was carrying a passenger list, had survived but was still too shocked to be questioned by police.
The bus and the truck carrying sugar had collided around 5:30 am (0530 GMT) six kilometres from Boromo, Compaore said earlier.
Burkia Faso's minister for social action, Pascaline Tamini, expressing profound sadness, offered the condolences of President Blaise Compaore, Prime Minister Tertius Zongo and the government.
Roads in West African countries are notoriously dangerous, especially at night.
In May, 46 Nigerian soldiers returning from an African Union peacekeeping mission in Darfur, Sudan, were killed in a collision between a petrol tanker and an army convoy.
In March 2007, 70 people travelling in the back of a truck were killed when the vehicle overturned while crossing a narrow wooden bridge in Guinea.