At least 36 people have been killed in Mexico after a bus burst into flames after crashing into a parked trailer truck.

The death toll could rise further but the fire made it difficult to identify all the bodies, Veracruz Governor Javier Duarte told Milenio television.

"The trailer-truck was on the shoulder of the highway...when the bus hit the back of the trailer, which caused this regrettable accident," he said.

"In addition to crashing, the bus caught fire, which makes the investigative work to identify bodies more difficult."

The accident took place as the bus took passengers from the southeastern Tabasco state city of Villahermosa to Mexico City.

The tragedy occurred as Mexicans are set to begin Holy Week in the predominantly Roman Catholic country.