A tsunami caused by an Indonesian earthquake late Monday night killed at least 113 people and left almost 200 others missing after it swept across villages on remote islands off the coast of Sumatra . Officials expected the death toll to climb as damage reports emerged.

Meanwhile, authorities scrambled to evacuate homes on the slopes of
Mt. Merapi , one of Indonesia 's most volatile volcanoes, on Java island, as it began to erupt late Tuesday. Several people were injured by hot ash spewed into the air and as many as 20 people were taken away for treatment, the Associated Press reported.

(This story and related background material will be available on The Wall Street Journal Web site, WSJ.com.)

The earthquake, measuring 7.7 in magnitude, struck 13 miles beneath the ocean Monday near the Mentawai islands. It initially was thought to have caused relatively little damage, triggering what was believed to be a small tsunami. But many of the damaged areas, including popular surfing spots, can take hours to reach from Sumatra , so the scale of the destruction still isn't fully clear.

The Indonesian government declared a state of emergency for tsunami-affected areas. Hendri Dori Satoko, the head of the regional government in the affected area, told local television that some of the missing people may have taken refuge on higher ground. Police on the Mentawai islands were searching for missing people and setting up emergency posts.

The head of the Health Ministry Crisis Center, Mudjiharto, who like many Indonesians goes by only one name, said medical personnel were on their way to the hardest-hit areas. The Indonesian welfare minister will fly Wednesday morning to monitor the relief work.

Indonesia has repeatedly faced earthquakes, eruptions and tsunamis over the years because of its location along a series of highly volatile fault lines known as the Pacific Ring of Fire. In December 2004, a tsunami caused by a magnitude-9 earthquake off Sumatra killed more than 226,000 people across Asia . It was the deadliest tsunami on record.