The 3,600-meter Mount Semeru in East Java Province erupted on Saturday. The eruption sent a mixture of hot ash and lava gushing into residential areas at the foot of the volcano.
Indonesia's National Disaster Mitigation Agency says that the death toll has risen to 22, and 56 people were injured. The agency also says 22 others are still missing.
The eruption has caused damage to about 3,000 houses near the mountain.
Video footage shows houses buried to their rooftops.
The National Search and Rescue Agency says the number of casualties may increase.
But its rescue operations have been hampered by bad weather, as workers try to dig up mud manually.
Professor Iguchi Masato of Kyoto University says that Mount Semeru is one of the most active volcanos in Indonesia.
He says that an eruption in 1994 also caused deaths, but the latest has caused even more extensive damage.