The eruption follows intense seismic activity and is classified as a fissure eruption, which does not usually result in large explosions or a significant amount of ash in the stratosphere, reports say.

The burst from the highest mountain on Indonesia's main island of Java prompted authorities to raise the alert status for the volcano to the highest level.

Four fissures have now opened up on the mammoth mountain, which burst into life on Sunday for the first time in almost 40 years.

Authorities bumped the threat of Anak Krakatoa to level three of a four-tier volcanic alert system after witnessing a sharp rise in activity in the last month.

At least three people were killed and survivors were left huddled under makeshift shelters.

Dozens of people remain missing.

Rescuers moved to evacuate local residents as lava reached nearby villages and destroyed a bridge in Lumajang regency in East Java.

The volcano, one of two currently erupting in Indonesia, remains at alert level three, the second-highest level.

The lava spewed by Mount Nyiragongo is particularly fluid and can move very fast.

It is unclear how many more bodies could be under the debris, or if there is anyone still trapped but alive more than two days after the disaster.

There were no reports of injuries or damage but residents have been warned to wear masks to protect themselves from the volcanic ash.

Merapi is one of the most dangerous volcanoes on Earth.