Java's Mt Kelud causes chaos
The eruption in east Java was so powerful it shot smoke 10km into the atmosphere. It sent gravel raining down as far as 50km from the crater of the volcano.
It was also preceded by an earthquake felt as far away as the central Java town of Solo, the Jakarta Globe reported.
Indonesian news website Tempo reported that Thursday night's eruption on the main Indonesian island could be heard as far away as Yogyakarta, 200km away.
A man and a woman, both in their 60s, were crushed to death after volcanic material from Mount Kelud blanketed rooftops, causing their separate homes in Malang to cave in, National Disaster Mitigation Agency spokesman Sutopo Purwo Nugroho told AFP.
"The homes were poorly built and seemed to have collapsed easily under the weight," he said.
About 200,000 people in a 10km radius from the volcano were ordered to evacuate, disaster officials said.
Many tried to return to their homes to gather clothing and valuables, but were forced back by a downpour of volcanic material.
TV images showed ash and rocks raining down on nearby villages. AFP correspondents at the scene saw terrified locals covered in ash fleeing in cars and on motorbikes towards evacuation centres.
The ash has blanketed the Javanese cities of Surabaya, Yogyakarta and Solo, where international airports have been closed temporarily, said the Transport Ministry's director general of aviation Herry Bakti. Metro TV showed images of grounded planes covered in ash.
Said Mr Bakti: "We will reassess the situation tonight regarding reopening the airports, but at the moment, it's too dangerous to fly anywhere near the plume."
On the outskirts of Yogyakarta, the authorities closed Borobudur, which is considered the world's largest Buddhist temple, after it was also rained upon with dust from the volcano. Usually, the site attracts hundred of tourists daily.
Virgin Australia said it had cancelled all its flights to Phuket, Bali, Christmas Island and Cocos Island yesterday, adding that the safety of customers was the highest priority.
Australian nurse Susanne Webster, 38, was on a late-morning Virgin flight from Sydney to Bali that was turned around.
"About two hours in, the pilot announced over in Indonesia there was a volcano that erupted and that we were turning the plane back," she told AFP.
AirAsia said it will cancel all flights to and from Surabaya, Semarang and Yogyakarta, The Star reported.
The 1,731m-high Mount Kelud is one of some 130 active volcanoes in Indonesia. It has claimed more than 15,000 lives since 1500.
Earlier this month another volcano, Mount Sinabung on western Sumatra island, erupted, leaving at least 16 people dead. It has been erupting almost daily since September.
Mount Kelud erupts
On the main island of Java, Indonesia
Thursday night. Two dead, about 200,000 evacuated
Deadly eruption sparks mass evacuations