MEXICO CITY - Protesters marched in the capital Thursday to demand authorities find 43 missing college students, seeking to pressure the government on a day traditionally reserved for the celebration of Mexico's 1910-17 Revolution.

Authorities canceled the traditional Nov 20 Revolution Day parade, but did not give a reason.

About 200 youthful protesters, some with their faces covered in masks or bandannas, scuffled with police as they tried to block a main expressway to the international airport. Protesters hurled rocks, fireworks and gasoline bombs at the police, at least one of whom was hit by the projectiles.

Some passengers had to walk to the terminal, but flights were not interrupted and expressways were reopened.

Many average people, outraged by the disappearances of the students after a clash with police in the southern city of Iguala, took part in more peaceful marches despite cold weather and a persistent drizzle.

"The entire country is outraged," said housewife Nora Jaime. "It is not just them," she added, referring to the 43 missing young men. "There are thousands of disappeared, thousands of clandestine graves, thousands of mothers who don't know where their children are."

Jaime clutched a Mexican flag on which the green and red stripes had been dyed black "as a sign of mourning." She said she joined Thursday's march because she fears her teenage son could share the same fate. "I am terrified to live in a country like this. I am terrified for my son."

Maria Teresa Perez attended the march holding aloft a poster with a picture of her son, Jesus Horta Perez, 45, who was kidnapped by armed men from a storefront in a Mexico City suburb in 2009 and has never been heard from again.

"They are shouting about 43, but they should be counting in the thousands, because apart from these 43, there are 33,000 disappeared," Perez said.

Parents like her have been forced by police inaction to investigate their children's fate themselves. "All the trails they have come from us, they don't do anything," Perez said of the police.

Mexico officially lists 22,322 people as having gone missing since the start of the country's drug war in 2006. And the search for the missing students has turned up other, unrelated mass graves.

Bus caravans carrying the relatives and family members of the 43 missing students converged on the capital after several days crisscrossing the country. The caravans were expected to head three march routes converging on Mexico City's main square.

The 43 students, who attended a radical rural teachers college, disappeared on Sept 26, when they went to Iguala in Guerrero state to hijack buses.

Iguala police intercepted them on the mayor's orders and turned them over to the criminal group Guerreros Unidos, a gang with ties to the mayor, prosecutors say.

Prosecutors say there is evidence the gang members killed the students and incinerated their remains, but the families have rejected that account and the marches were intended to keep pressure on the government to find them.

Prosecutors have sent badly burned bit of bone and teeth found at a garbage dump in Guerrero to a laboratory in Austria to see if any DNA samples can be recovered to help identify the remains.