On Monday the volcano in the Sunda Strait spewed hot lava and other volcanic material 2,000 feet above its peak, the Antara news agency reported.
"Tremors have not stopped rocking this area since yesterday," Hamdani, the head of the volcano monitoring post in the village of Hargopancuran, South Lampung, said.
Black clouds were obscuring the peak of the volcano, Hamdani said.
Officials warned fishermen to stay away from the volcano although they said the ongoing tremors would not cause a tsunami.
"But it is difficult to predict Anak Krakatau," Hamdani said.
Krakatau's explosion in the 18th century, so loud it was heard 1,000 miles away, caused one of history's most devastating tsunamis.