The aviation alert for the erupting volcano at Anak Krakatoa has been upgraded to red and Indonesia is rerouting flights amid fears of another eruption.
A tsunami triggered by the collapse of the crater on Saturday killed at least 430 people and cuased widespread damage.
Residents have been urged to stay away from the coast after authorities raised the fears of another collapse and resultant tsunami.
Indonesia ’s national geographic agency raised the alert level to the second highest and has ordered a 5km exclusion zone around the island.
An official said activity at the crater had not sopped since December 23 and anticipated "a further escalation".
The nation's air traffic controller, AirNav, said it was rerouting aircraft around the ash cloud.
No airports have been affected but some flights could take longer because of the changes.
Indonesia’s capital, Jakarta, is about 155kms to the east of the island.
A Volcano Observatory Notice for Aviation (VONA) issued Thursday upgraded the warning from orange to red.
It said the best estimate of the height of the ash cloud was 23, 482ft above sea level but warned it may be higher than could be observed clearly.
The cloud was moving to the northeast, it said.
Anak Krakatoa (Child of Krakatoa) emerged in 1927 from the remnants of Krakatoa which, in 1883, underwent the most violent volcanic eruption in recorded history.
That eruption, which was heard thousands of miles away, killed more than 30,000.
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