The number of musicians apparently topped the previous record of 700 mariachis at an earlier gathering in the Mexican city of Guadalajara.
The Guinness World Records organization hasn't replied to a message from The Associated Press asking whether Sunday's gathering broke the previous record.
The musicians, many of whom had arrived in Mexico's capital from other cities, expressed their joy at singing in the giant iconic plaza, saying the music is a family tradition they start learning at a young age.
Jesús Morales said his father taught him to play the violin at age 8, and at 13 he began playing with his uncles in the Mariachi Morales in the city of Hidalgo.
"The heritage that my dad mainly instilled in us is having respect for music and respect for our roots," he said.
The mariachis played guitars, trumpets, violins and other instruments.
Aida Juárez is a mariachi with 20 years of experience. She is a pioneer of women's mariachi groups.
"We feel proud that we broke (the record), it is a pride because we are Mexicans," she said.
Diana Rocío Campos is a merchant who attended the event and loves the music.
"Anyone who listens to (the mariachi) gets very excited, whether they are Mexican or not," she said. "People come from many countries like Colombia or Japan" to listen to the mariachis.