11 people were killed while three men were treated in intensive care for burn injuries Saturday after being engulfed in scorching clouds from Indonesia's Mount Sinabung in its biggest eruption in recent days, officials said.

Mount Sinabung on the western island of Sumatra had shown a reduction of activity since mid-January.

But it erupted again on Saturday morning, sending hot rocks and ash up to 2,000 metres (16,000 feet) into the air, blanketing the surrounding countryside with grey dust, said volcanologist Kristianto, who like many Indonesians goes by one name.

A man and his son were caught by the clouds when they went to Sukameriah village, 2.7 kilometres (1.7 miles) south of Sinabung crater to pay respect at the graves of their relatives.

Another man who came to the village to check his long-abandoned house, was also trapped and injured by the deadly clouds which swamped the village, officials said.

"While they were there, Sinabung erupted and spewed hot clouds. They did not manage to escape," Karo district official, Johnson Tarigan, told AFP.

He said the three were in an intensive care unit of a local hospital.

Thirty-thousand people have taken refuge since the volcano started erupting in September.

Some have returned home on Friday following advice from the Center for Volcanology and Geological Hazard Mitigation that houses outside the five-kilometre radius from Sinabung are safe.

Mount Sinabung is one of 129 active volcanoes in Indonesia that straddle major tectonic fault lines, known as the Pacific Ring of Fire.

It had been quiet for around 400 years until it rumbled back to life in 2010, and again in September last year.

In August 2013, five people were killed and hundreds evacuated when a volcano on a small island in East Nusa Tenggara province erupted.

The country's most active volcano, Mount Merapi in central Java, killed more than 350 people in a series of eruptions in 2010.