The coach was carrying a club of elderly people on an excursion when it collided with the lorry near the village of Puisseguin, east of Bordeaux in south-west France.
According to emergency workers and local authorities in the department of Gironde, many of the victims died in the fire and images being broadcast on French television showed the coach as a charred shell that had been entirely burned out.
Eight people managed to escape the burning coach and four of them suffered serious burns.
The driver of the coach was among the survivors.
On Friday afternoon it was revealed that the body of a three-year-old child, believed to be the driver's son, was discovered in the lorry's cab.
The crash was the deadliest in France since August 1982 when 53 people including 44 children were killed in a motorway pile-up.
France's Prime Minister, Manuel Valls visited the scene of the crash on Friday.
"We wish, of course, to express our sorrow, our compassion and our support ... to all the families and those close to the victims," he said. "This is an horrific catastrophe, the likes of which we have not seen on the roads in more than 30 years. It is a terrible shock this region, la Gironde, Aquitaine, and a terrible shock for France. And today France, and the French, are in mourning".
The coach had left a small village nearby.
Reports say the bus slid into a bend and possibly the truck was driving in the bus-lane when they collided and burst into flames.
Some 60 firefighters and 20 fire engines were then dispatched to the scene.
The accident has sparked a new debate on road safety in France.
Local Socialist MP Gilles Savary on Friday blamed the drivers not the roads.
"These are very narrow roads but many French roads are narrow," he said. "France has many small roads linking villages in its road network, and these little roads can be extremely picturesque. It would be unreasonable to blame the roads, drivers must be in control of their vehicles in all circumstances."
The French parliament observed a minute of silence in honour of the victims on Friday.