One political scientist, says the most volatile volcano Indonesia has started to break, spitting plumes of hot ash and rock into the air.
Several people were injured by hot ash spewed by the eruption of the first. An AP reporter saw at least 20 people were removed for the treatment of wounds.
Subandriyo, regional chief volcanologist said the eruption of Merapi began shortly before dawn on Tuesday. He grumbled and groaned hours.
Scientists have warned that the pressure Merapi lava dome building could trigger one of the most powerful explosions in many years.
Thousands of residents were evacuated on the runway.
Scientists had warned earlier in the day, under the pressure of the lava dome in the construction of the mouth of the volcano more birds in Indonesia could lead to an explosion of the deadliest in years.
Meanwhile, another city in a disaster has occurred elsewhere in the country on Tuesday, authorities said the death toll from a tsunami in western Indonesia has risen to 23, and dozens of people were missing.
The wave of 10 feet was a 7.7 earthquake struck 13 miles beneath the seabed size at night on Monday night. A tsunami watch was issued for the islanders in the area immediately after the earthquake, but was canceled an hour later.
Merapi has been increased volcanic activity in recent days, after officials at the alert level to 9,737 meters high mountain at the highest level of increase, the spokesman said the government volcanologist who uses only one name Surono.
Its last eruption was in 2006 when an avalanche of falling bubbles of gas and rock fragments of mountain race that left two dead. A similar outbreak in 1994 killed 60 people, while 1,300 people died in an outbreak in 1930.
An avalanche of rocks buried beneath the slopes of Merapi early Tuesday shaking explosions of ash and hot shot 150 feet into the air as the mountain rumbled and groaned.
The main concern Surono told reporters he was building pressure behind a lava dome that has formed near the crater.
"The energy is building. ... We hope that slow," he said. "Otherwise, we are looking for a possibility of huge explosion, bigger than anything we've seen in years."
Sri Purnomo, head of the district of Sleman, the island of Java, Mount Merapi is said that the authorities were warned about 11,400 residents on the southern side of the mountain in preparation of the "evacuation".
Hundreds of people have been moved to makeshift camps in government buildings and sports fields for more than six miles from the mountain's base, many of whom were elderly and children.
"I'm here to follow orders only to flee for safety, but I'd rather stay home," said Ponce Sumarto, 65, who became one of the fields with her two grandchildren.
She said that her children stayed at home to take care of animals and plants to be taken.
There are over 129 active volcanoes in Indonesia, spread over 17,500 islands and is prone to eruptions and earthquakes because of its location in the "Ring of Fire" to see - a series of failures in the Western Hemisphere through Japan and Southeast Asia .
The youngest was Mount Sinabung in the province of North Sumatra. It is idle for four centuries, but before jumping to life in August and settled along the slopes and refugees have returned home.
Meanwhile, a strong earthquake Monday off the west coast of the Indonesian island of Sumatra, but no damage or injuries were immediately reported.
The earthquake of magnitude 7.5 hit at a depth of six miles on a small island of Sumatra, said U.S. Geological Survey. An earthquake and tsunami of the same island in 2004.