The meteorology agency that an area of about 64 hectares, or 90 soccer pitches, of the volcanic island had collapsed into the sea.

In 1883, the volcano then known as Krakatoa erupted in one of the biggest blasts in recorded history, killing more than 36,000 people in a series of tsunami, and lowering the global surface temperature by one degree Celsius with its ash. Anak Krakatau is the island that emerged from the area in 1927, and has been growing ever since.

The high waves isolated hundreds of people on Sebesi island, about 12 km from the volcano.

"We are completely paralysed," Syamsiar, a village secretary on the island, told Metro TV, calling for food and medicine.