The centre said in a press statement on December 29 that the volcano now stands 110 meters high, down from 338 m in recent months.
According to the centre, which is based in the West Java provincial capital of Bandung, the position of Mt. Anak Krakatau's peak is now lower than the nearby islands of Sertung and Panjang.
The centre also said Mt. Anak Krakatau has lost between 150 million and 170 million cubic meters of its volume, with only between 40 million and 70 million cubic meters remaining.
"Anak Krakatoa is now much shorter, usually you can see the peak from the observatory post, now you can't," said Wawan Irawan, a senior official at the agency.
Before and after satellite images taken by Japan's space agency showed that a two square kilometre chunk of the volcanic island had collapsed into the water.
The eruption of the volcano on December 22 caused the southwestern flank of its caldera to collapse, causing underwater landslides that triggered a tsunami that hit nearby coastlines of Java and Sumatra.
A total of 431 people are confirmed to have died as of December 29, with 15 others still missing and 7,202 injured. Nearly 47,000 people have been displaced.
Given the volcano's remaining low volume, the agency said the possibility of another tsunami being triggered by an eruption is low.
On December 27, the centre raised the alert status of the volcano due to increased activity to Level 3, one notch below the highest level. It recommended that locals and tourists not be allowed within a radius of 5 kilometers of the peak.
Volcanic activity at Mt. Anak Krakatau has been on the increase since June, with almost daily eruptions.
It is the product of the infamous Krakatau, whose tsunami-triggering eruption in 1883 was one of the largest of modern times, killing more than 36,000 people and leaving a massive crater in which grew Mt. Anak Krakatau, or "Child of Krakatau."-VNA