The 2,963 metre-high (9,721 feet) Merapi is one of Indonesia's most active volcanoes and was already on the country's second-highest alert level.
Official at local monitoring post, Yulianto said no residents have been evacuated.
"This has only been observed as one time event, there have been 5-6 avalanches. If the coverage continue to increase and the distance is further than 7 kilometres, it is likely that the residents will be recommended to evacuate," he said.
Located on the Pacific Ring of Fire, Indonesia has more volcanoes than any other country. Merapi last violently erupted in 2010, killing more than 350 people.
