The mountain is located in North Sulawesi, and the eruption spewed volcanic debris and ash into the atmosphere more than a mile high.
Because of lack of visibility and the potential dangers of ash to aircraft, both the Sam Ratulangi Airport in Manado and Djalaludin Airport in Gorontalo have been shut down until 4 pm local time.
The Indonesian geological service has issued an alert at the highest level and is urging climbers as well as residents to distance themselves at least around 4 miles from the volcanic crater. Over 12,000 have been evacuated including the over 800 residents who live on Ruang island.
The Center for Volcanology and Geological Hazard issued a warning of a possible tsunami for Tagulandang island due to volcano debris falling into and disrupting the ocean waters.
This is the second eruption of Mount Ruang in the past 2 weeks.