Protesters on Sunday clashed with police in the southern Mexican state of Guerrero during an attempt to organize a concert in support of the 43 missing students from the Raúl Isidro Burgos Rural Teachers' College of Ayotzinapa.

According to the Guardian, students from the Ayotzinapa teachers’ college assembled in the early morning to block a street with metal barriers for the concert.

The blocked street happened to lead to the hotel where federal police were staying, and that’s when the trouble began.

At least 21 people were injured, and several cars were left in flames.

A police official claimed that eight officers were injured, a number which includes five officers who were run over by a vehicle and three that were said to have been beaten by protesting teachers. One of the officers was left with severe brain damage.

The Tlachinollan human rights group states that the ensuing violence has left at least 13 people injured, including students, teachers, parents of the missing students and several journalists, including an Associated Press photographer.

Each side has blamed the other for starting the clash in Chilpancingo that ended in mayhem and injury.

Since the 43 missing students went missing, there have been constant and, for the most part, peaceful protests, and there have been resulting political changes as well. The Mexican President Enrique Peña Nieto has called for sweeping police change to come over the next two years as the Mexican security forces are seen as thoroughly corrupt.

Mexico’s attorney general said 80 people have been arrested so far in the case, including 44 police officers from the cities of Iguala and Cocula and even the former Iguala Mayor Jose Luis Abarca and his wife Maria de los Angeles Pineda.