Residents said rumblings associated with the eruption shook their windows and sounded like cannon fire.
Chunks of molten lava could be seen shooting from the summit crater as ash soared three miles into the sky over the Andes.
Schools in nearby Baños were closed as volcanic ash rained on the town.
Tungurahua roared to life in 1999 after a long period of slumber.
An eruption in 2006 left four people dead, two missing and large tracts of farmland destroyed.
Photo: Instituto Geofisico de Ecuador