Abbas Gullet, secretary general of the Kenyan Red Cross, says "more than 50" people died after a crowd gathered around the crash in search of free fuel. Reuters is reporting 111 dead: 91 at the scene and another 20 taken to a local mortuary, according to a provincial police commissioner.
The crash was in Molo, several hours outside the capital, Nairobi.
Local newspapers have criticized the government for poor safety.
On Wednesday, a massive fire swept through a supermarket in downtown Nairobi, killing at least 25 people.
After the supermarket blaze, the Daily Nation said Nairobi's 3 million people are served by just one fire station situated close to a traffic-choked business district.
"Ours is a modern city with an 18th-century firefighting infrastructure," the newspaper said in an editorial.