Indonesia raised the alert status of the Mount Merapi volcano to the highest level on Saturday, prompting a compulsory evacuation of thousands of residents living on the slopes, officials said.
"This morning we raised the status of Merapi to the top alert, which is the red code. Every resident has been ordered to evacuate," Subandrio, head of the Merapi section at the Centre for Volcanological Research and Technology Development, told Reuters.
Residents said they could see lava flowing and thick smoke rising from Merapi, onef the most dangerous volcanoes in the Pacific "Ring of Fire" that has been rumbling for weeks.
"I could see the lava clearly from my home this morning. Then they ordered us to evacuate our village," said Anton, a 25-year-old resident of Boyong village, around 8 km (5 miles) from Merapi.
Television footage showed lava flowing out of the crater while thick clouds of smoke rose upwards and a large fireball burst into the night sky.
Despite the increased seismic activity and the lava which had flowed around 1.6 km (1 mile) from the volcano's crater, Subandrio could not say when the volcano was likely to erupt.
Dali, another vulcanologist, told Reuters the top alert - also known as code red or 'danger' status - meant that technically the mountain could erupt within the next 24 hours.
Merapi, which means "Mountain of Fire", lies near the ancient city of Yogyakarta at the centre of densely populated Java island. It killed 70 people in a 1994 eruption and 1,300 in 1930.
Government officials along with army and police evacuated more than 5,000 people living near the volcano to tents and shelters in safe areas following the new alert level.
The local government has been struggling to conduct mass evacuation as some villagers living on the slopes refuse to be moved because they rely on natural signs rather official orders.