A Costa Rican volcano began to erupt overnight, spewing ash that has reached the nation’s capital city.

Turrialba volcano is located 30 miles east of San Jose  Seismic activity began on Wednesday night before what volcanologists say is the biggest eruption of the volcano in at least a century.

Officials have been evacuating villages around the volcano in anticipation of lava flow.  Ash was falling in at least four provinces from the eruption.

“We are maintaining 24/7 vigilance at our seismic stations,” Gino Gonzalez of the country’s National Seismological Network told AP.

Aircraft have been ordered to stay more than 20 miles from the volcano site and if it must cross through the area to stay over 18,000 feet.