The dawn accident near Kasserine also left around 15 cars ablaze, according to the ministry.
It said the lorry driver, who was among those killed, was unable to brake and his vehicle hit the bus and several cars before slamming into an electricity pole.
Dozens of injured were taken to hospital in Kasserine, as emergency crews worked to extract others still trapped in the wreckage.
Photos shared on social media showed columns of thick black smoke rising from the scene of the accident, and national television broadcast images of burnt cars.
As of the end of May, 528 people had died in road accidents in the North African country of around 11 million inhabitants since the start of the year.