Tens of thousands of people angry at the presumed massacre of 43 students have marched in Mexico City, many chanting for President Enrique Pena Nieto's resignation.
Protesters waved blackened flags of Mexico and chanted "He will fall, he will fall, Pena Nieto will fall!"
Parents of the 43 male college students, who reject claims their sons are dead, led the march along the capital's main boulevard toward the historical Zocalo square.
It was the latest protest over the government's handling of a crime that has infuriated Mexicans fed up with corruption, impunity and a drug war that has left more than 100,000 people dead or missing since 2006.
The case has turned into the biggest challenge of Pena Nieto's nearly two-year-old presidency, on top of another scandal over a mansion his wife bought from a government contractor.
"Mexico is used to tragedy, robberies and corruption, and we need to begin to exercise our rights as citizens to get the government working," said Lili Correa, 46, wearing the black colour of the protest.
The demonstration coincided with the anniversary of the start of the 1910 Mexican revolution.
The government cancelled the annual parade.
Before the march, masked protesters threw firebombs and used tubes like makeshift bazookas to launch firecrackers at riot police, who hit back with tear gas to disperse the group on a street near the airport.
The clash came after hundreds of protesters blocked the main road to the airport for an hour, while police vehicles picked up passengers walking with their suitcases along the road.
Thousands of people also marched in the cities of Ciudad Juarez, Puebla and Chilpancingo, the capital of Guerrero, the violence-plagued southern state where the students vanished nearly two months ago.
Mexico and Real Madrid football star Javier "Chicharito" Hernandez tweeted a picture of himself wearing a black hoodie and the hashtag #WeAreAllAyotzinapa, referring to the young men's Ayotzinapa teacher-training college.
"The goal is to unite and mobilise the country, to lead it toward change," said Omar Garcia, who attends the college.
With the annual parade called off, Pena Nieto led a ceremony with top officials at the Campo Marte military field, where he and the defence minister denounced violent protests.
"Mexico is hurting, but the only path to soothe this pain is through peace and justice," he said, hours after making his personal assets public to quell conflict of interest allegations over his wife's mansion.
The crisis erupted after the mayor of the city of Iguala ordered police to confront students on September 26, sparking a night of violence that left six people dead and 43 missing, authorities say.
Prosecutors say corrupt police delivered the 43 young men to members of the Guerreros Unidos drug gang, who confessed to killing and incinerating the students.
Officials stopped short of declaring the students dead pending DNA tests.
Federal police teams continue to search for them in Guerrero.
Buses carrying parents of the missing young men joined the march after a week-long tour of the country to voice their anger over the government's handling of the case.
Highlighting their deep distrust of the government, they refuse to believe the students are dead and say they will only trust DNA test results from independent foreign forensic experts.
