JAKARTA (AFP) - An Indonesian volcano known as the "child" of the legendary Krakatoa erupted on Thursday (July 19), spewing a plume of ash high into the sky as molten lava streamed down from its summit.

Anak Krakatau - a small volcanic island that emerged from the ocean a half century after Krakatoa's deadly 1883 eruption - has rumbled back to life in recent weeks, spitting flaming rocks and ash from its crater.

No one lives on Krakatau, which forms a small island in the Sunda Strait between Java and Sumatra, but the peak is a popular tourist spot.

Indonesia's geological agency has not raised the alert level for the mountain. However, there is a one kilometre no-go zone around its summit.

When Krakatoa erupted in the 19th century, a jet of ash, stones and smoke shot more than 20km into the sky, plunging the region into darkness, and sparking a huge tsunami that was felt around the world.

The disaster killed more than 36,000 people.

Indonesia is situated on the Pacific "Ring of Fire", a vast zone of geological instability where the collision of tectonic plates causes frequent quakes and major volcanic activity.