Indonesia hikes danger level for deadly tsunami volcano

Indonesia on Thursday raised the danger alert level for a volcano that sparked a killer tsunami at the weekend, after previously warning that fresh activity at the crater threatened to trigger another deadly wave.

Authorities also widened a no-go zone around Anak Krakatoa to five kilometres (three miles) -- up from a previous two kilometres -- and warned shell-shocked residents to stay away from the coast, after more than 400 were killed by Saturday night's killer wave.

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.

Authorities raised the crater's status to high alert, the second-highest danger warning, while aviation officials ordered flights to be redirected away from the area.

"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.

"This worries me," said Ugi Sugiarti, a cook at the Augusta Hotel in hard-hit Carita. "I've already left."