(CNN) At least 75 inmates escaped from a prison in Paraguay through an underground tunnel Sunday, the Ministry of Interior's Office said in a statement.

The majority of the escapees belonged to a criminal Brazilian gang known as the "PCC" -- the Primeiro Comando da Capital, or the First Capital Command.

Interior Minister Euclides Acevedo described them as "highly dangerous" prisoners and said some of them may have already crossed over to Brazil.

He said police in Pedro Juan Caballero, the town bordering Brazil where the prison is located, are on "maximum alert" after the "massive" prison break.

The PCC -- a powerful prison gang -- is the "largest and best-organized criminal organization in Brazil," according to InSight Crime , a foundation that studies organized crime in the Americas.

Read More