National Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho said the minor eruption on the Indonesian tourist island began about 5:05pm local time (8:05pm AEDT) Tuesday, confirming the plume rose about 700 metres from the volcano.
Authorities say the alert level remains unchanged, with volcanologists blaming the eruption on magma heating water. Eruptions involving magma are generally considered more dangerous, Mr Nugroho said.
Agung's alert status was recently lowered to the second-highest warning level after spending several weeks at the highest level.
More than 140,000 people evacuated the region around the volcano when it was on high alert, though authorities urged those who had left areas not in the official danger zone to return home.
Residents have been urged to remain calm.
'Do not panic. Stay away from areas within a six-and-a-half to five kilometre radius of the volcano,' the National Disaster Mitigation Agency.
Bali's international airport remains open despite the eruption.