The volcano located in Indonesia's Yogyakarta special region erupted around 12 p.m local time (0500 GMT) and a lava flow of 1.5 km was observed, the local authority said, according to Reuters.
Residents in the nearby community have been warned to stop any activities in the danger zones, range between three to seven kilometers radius from the crater, the statement said.
The 2,963 meter-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 kilometers, it is likely that the residents will be recommended to evacuate," he said.
SKH/PR