Angry protesters rallying against the alleged killing of 43 Mexican students have clashed with riot police in Acapulco as authorities downplayed chances of ever identifying their remains.

Thousands of people rallied in front of the resort's international airport on Monday, with parents of the students leading the demonstration along with comrades from the 43 young men's teacher-training college in the southern state of Guerrero.

A group of masked protesters clashed with riot police who had tried to block their way to the airport, injuring 11 officers, a public security official said.

After negotiations, the protesters were allowed to go through.

Many protesters were armed with bats, metal pipes and machetes in the latest demonstration over a case that has angered Mexican society and turned into the biggest crisis of President Enrique Pena Nieto's administration.

"Ayotzi lives, the struggle goes on," the protesters chanted, referring to the missing students' Ayotzinapa teacher-training college.

Tourists had to reach the airport by foot, pulling their suitcases behind them.

On Saturday, thousands of people marched in Mexico City, the capital, where a group of 20 protesters briefly set fire to the door of the National Palace, which Pena Nieto uses for official ceremonies.

Authorities say that on September 26, police in Iguala shot at buses carrying the students and handed them over to the officers in the neighbouring town of Cocula, who then delivered them to the Guerreros Unidos drug gang.

Officials say authorities say Jose Luis Abarca, the mayor of Iguala at the time, ordered the officers to confront the students over fears that they would derail a speech by his wife, who was the head of the town's child protection agency.

Abarca and his wife were arrested in Mexico City earlier this month after going oh the run.

The demonstrations came after authorities announced on Friday that gang suspects had confessed to killing the 43 students, incinerating their remains and tossing them in a river after receiving them from corrupt police.

Attorney General Jesus Murillo Karam warned that only two bones were salvageable for DNA tests.

Source: Agencies