At least 26 people were killed and 22 others injured in a bus accident on Sunday in the southwestern Mexican state of Guerrero, local authorities said.

The accident occurred at around 1:30 p.m. local time (1830 GMT) in a highway between the towns of Tlamacazapa and Buenavista de Cuellar when the bus overturned and plunged into a 200-meter-deep ravine, said Guerrero State Civil Defense Secretary Constantino Gonzalez Vargas.

According to local media, all the victims are members of the Democratic Revolution Party (PRD) and Workers' Party (PT), who were heading to a rally to be held in Buenavista de Cuellar.

Rescuers, paramedics and firefighters rushed to the scene to help the victims while traffic was suspended along the highway to facilitate rescue efforts.

The injured were taken to nearby hospitals in the towns of Taxco, Iguala and Buenavista de Cuellar.

Carlos Reyes Torres, the state leader of the PRD, lamented the tragedy and said the victims were heading to Buenavista to support the PT's candidate for the municipal elections Elias Salgado.

The PRD's National President Jesus Zambrano also regretted the accident and expressed his solidarity with the families of the victims.

Mexico's Interior Minister Alejandro Poire has called the PT leader to offer his condolences.