The bus, travelling from the capital Phnom Penh, swerved into the truck after its front tyre exploded on a road in Battambong province, said Sath Kimsan, chief of provincial traffic police.
"Eight people, including a woman and a Buddhist monk, died on the spot," he told AFP.
The injured were rushed to nearby hospitals, he said.
"The front tyre on the left side of the bus exploded while it was driving at a fast speed," said the officer, adding that both drivers were killed in the collision.
Cambodia's roads are notoriously dangerous with around 2,000 people dying in accidents annually.
Last August, 16 Cambodians were killed and 23 others injured after a bus plummeted off a mountain road near the Thai border.