A bus has crashed into the back of a badly parked lorry and burst into flames in Mexico, killing at least 36 people and injuring four others, authorities say.

Most of the roof and tyres of the bus were reduced to ashes by the highway accident on Sunday in the southeastern state of Veracruz, according to television images.

"The trailer-truck was on the shoulder of the highway at kilometre 135 when the bus hit the back of the trailer, which caused this regrettable accident," Governor Javier Duarte told Milenio television.

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

Federal police concluded that the lorry was badly parked, the state government said. A state prosecutor was sent to investigate the crash, the AFP news agency reported.

At least 36 people were confirmed dead, Alberto Silva Ramos, said government spokesman, said. Duarte had earlier reported 25 deaths.

Those injured have been hospitalised and are in stable condition, officials said.

Both state and federal officials said that four people survived the crash, which occurred shortly after midnight in the southeastern state of Veracruz.

A communique from the state civil defence agency said the victims were business people from the region who were travelling from the Tabasco state capital of Veracruz to Mexico City.

President Enrique Pena Nieto expressed his "deepest condolences" to the families of the victims via Twitter.

Source: Agencies