Ash soared more than 15,000 feet into the sky and rained down on the nearby towns of El Viejo, El Concho and Rancheria, according to the Nicaraguan Institute of Territorial Studies (INETER).
The agency said that activity within San Cristobal had subsided considerably, but could still produce further blasts.
The 5,740-foot volcano is located about 90 miles northwest of Managua and has been active since at least 1520.
INETER reported that two other volcanoes, Telica and Apoyeque, had shown signs of unrest in recent weeks.
Photo: Nicaraguan Institute of Territorial Studies