Indonesia has rerouted all flights around the erupting Anak Krakatau volcano between Java and Sumatra islands, as it spewed columns of ash into the air, days after it triggered a deadly tsunami.
Plumes of ash burst into the sky as pyroclastic flows -- hot gas and other volcanic material -- flowed down the crater, raising the risk of rough seas for boats in the vicinity.
A crater collapse on the volcanic island at high tide on Saturday sent waves up to 5 metres high smashing into the coast on the Sunda Strait, killing more than 400 people.
"All flights are rerouted due to Krakatau volcano ash on red alert," the government air-traffic control agency AirNav said in a release on Thursday.
Authorities raised the volcano's alert level to the second-highest on Thursday, imposing a 5 km exclusion zone.
"We've raised the status of (the volcano) since this morning because there's been a change in the eruption pattern," Kus Hendratno, a senior official at the Krakatoa observatory, told AFP Thursday.
The new flows posed no immediate danger to area towns as the volcano sits in the middle of the Sunda Strait between Java and Sumatra islands.
But the status change sparked new fears with many local residents already scared and refusing to return to their communities over fears of another tsunami.
An aerial view shows mount Anak Krakatau erupting in Lampung, Indonesia, 23 December. Source: EPA
"This worries me," said Ugi Sugiarti, a cook at the Augusta Hotel in hard-hit Carita. "I've already left."
Sukma, a security guard at the shattered Mutiara Carita Cottages, added: "Just please pray for us and that everything will be okay."
A section of the crater -- which emerged at the site of the Krakatoa volcano, whose massive 1883 eruption killed at least 36,000 people -- collapsed after an eruption and slid into the ocean, triggering Saturday night's killer wave.
At least 430 people were killed, with 1,495 people injured and another 159 were missing.
Nearly 22,000 people have been evacuated and are living in shelters.
Indonesia, a vast Southeast Asian archipelago, is one of the most disaster-hit nations on Earth due to its position straddling the so-called Pacific Ring of Fire, where tectonic plates collide.
