AP, Jakarta :
Indonesia raised the alert status of the Anak Krakatoa volcano to the second-highest level on Thursday morning, imposing a 5km exclusion zone.
This comes days after a crater collapse on the volcanic island at high tide sent waves up to 5m (16 feet) high smashing into the coast on the Sunda Strait, killing more than 400 people.
Authorities have also rerouted all flights around the erupting volcano as it spewed columns of ash into the air.
The volcano has been rumbling on and off since July but has been particularly active since Sunday, spewing lava and rocks, and sending huge clouds of ash up to 3,000m into heavily overcast skies.
“All flights are rerouted due to Krakatoa volcano ash on red alert,” the government air-traffic control agency AirNav said in a release.
Meanwhile, national disaster agency spokesman Sutopo Purwo Nugroho said: “The volcanic activity of Anak Krakatoa volcano located in the Sunda Strait continues to increase.”
“To that end, the Volcanology and Geological Disaster Mitigation Centre (PVMBG) has upgraded the status of Anak Krakatoa volcano from Level 2 (Alert) to Level 3 (Standby),” he said.
Indonesia has a four-level alert system for volcanoes.
Mount Agung, which recently erupted in June and caused hundreds of flights to be disrupted, was at the highest alert of Level 4.
All people and tourists have been prohibited from carrying out activities within a 5km radius of the volcano’s crate peak, said Mr Nugroho. This is because eruptions in the form of incandescent rocks, hot clouds and thick volcanic ash can be dangerous.
Indonesia’s meteorology agency has also recommended that no activities should be held on the coast at a 500m to 1km radius from the coast in anticipation of a subsequent tsunami.
“People are encouraged to remain calm and increase their awareness. Always use information from PVMBG for volcano early warning and the meteorology agency (BMKG) regarding tsunami early warning as an official institution.” said Mr Nugroho.
“Do not believe in misleading information whose sources cannot be accounted for,” he added.
A thin layer of volcanic ash has been settling on buildings, vehicles and vegetation along the west coast of Java since late on Wednesday, according to images shared by the national disaster mitigation agency.
Authorities said the ash was not dangerous, but advised residents to wear masks and goggles when outside.
On Wednesday, authorities warned of “extreme weather and high waves” around the erupting Anak Krakatoa volcano.
BMKG said late on Tuesday the rough weather around the volcano could make its crater more fragile.
“We have developed a monitoring system focused specifically on the volcanic tremors at Anak Krakatoa so that we can issue early warnings,” said BMKG head Dwikorita Karnawati, adding that a 2km exclusion zone had been imposed.
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.
