The San Cristobal volcano roared to life with three explosions Saturday, government spokesman Guillermo Gonzalez said.
Ash and gases from the volcano were blasted more than 2 miles upward from the 5,700-foot mountain, some 80 miles north of the capital, Managua, CNN reported.
The mandatory evacuation of people living on the mountain began within minutes of the first explosion, officials said.
Government emergency officials said as many as 20,000 people could be affected by the fall-out from the volcano, but no other evacuations had been announced by midday Sunday.
The volcanic mountain is Nicaragua's highest and last erupted in 2011, the report said.