National disaster agency spokesman Sutopo Purwo Nugroho said 745 people were injured and 30 were missing.
“This number will continue to rise considering not all places have been checked,” Dr Sutopo told a media briefing in Yogyakarta.
The tsunami slammed without warning into tourist beaches and coastal areas around Indonesia’s Sunda Strait on Saturday night, sending panicked holidaymakers and residents fleeing.
Hundreds of buildings were destroyed by the wave, which hit the coast of southern Sumatra and the western tip of Java about 9.30 pm (1430 GMT) following the eruption of a volcano known as the “child” of the legendary Krakatoa, national disaster agency spokesman Sutopo Purwo Nugroho said.
Search and rescue teams were scouring rubble for survivors, with at least 584 people injured and twenty reported missing across three regions.
Images broadcast on television showed the wave pushed a tangled mess of corrugated steel roofing, timber, rubble and flotsam inland from the coast at Carita beach, a popular day-tripping spot on the west coast of Java.
Authorities said the tsunami may have been triggered by an abnormal tidal surge due to a new moon and an underwater landslide following the eruption of Anak Krakatoa, which forms a small island in the Sunda Strait between Java and Sumatra.
“The combination caused a sudden tsunami that hit the coast,” Nugroho said, but added that Indonesia’s geological agency was working to ascertain exactly how it happened.
“We saw hundreds of people who were watching a music event disappear under the wave,” Nono, a tourist from Bekasi, West Java, said as quoted by Antara news agency on Sunday.
Among the tourists on the beach were employees of state utility company PLN and civil servants from the Youth and Sports Ministry. They were gathered around a stage watching a performance of dangdut music, he said.