The crash occurred late Thursday as the minibus was travelling from Switzerland to Portugal, taking the passengers home for the Easter holidays.
"The 12 passengers of the minibus, who were all Portuguese, are dead," said a statement from the local authority.
Authorities said the minibus swerved for an unknown reason and slammed head-first into the truck on a notorious traffic blackspot near the town of Moulins.
The minibus driver and two Italian drivers of the truck suffered injuries but are expected to survive.
An initial inquiry said the driver of the minibus was not under the influence of alcohol, and police have opened an investigation into the cause of the crash.
The accident took place on a portion of the Centre-Europe Atlantic Road which crosses the whole of France from east to west.
There are so many accidents on the highway that locals have nicknamed it "the road of death".
Local newspaper La Montagne reported that the number of deaths on the road is five times the national average.
The road "is quite monotonous, the speed limit is 90 kilometres (55 miles) per hour. There are those who are impatient and those who fall asleep," said a source close to the investigation, adding that there are only four passing zones in the area.
"They've been talking about adding a second lane for 40 years," he added.
A local official told AFP: "It's the deadliest road in France. When you add it up, we've had 15 deaths in a year."
Gerard Deriot, head of the regional council of Allier where the accident took place, said he was "appalled" to see more deaths on the road.
"It is appalling when, for years you have pushed the state to assume its responsibilities" and upgrade the road, said the politician, a representative of the opposition Republicans party.
Secretary of State for Transport Alain Vidalies said more than 100 million euros ($111 million ) had been set aside in 2016 to upgrade the road.
A local village hall was being used as a temporary morgue.
The road was closed following the accident, and was expected to remain shut until 9:00 am (0800 GMT) Friday.
The crash comes after after two school bus accidents in February left eight dead in France.